Is there any way I can gauge my IT knowledge to better help me find where I am weakest and strongest to get a higher end position?

You will also see many other certification routes available on the above websites for specialalities other than the Microsoft ones I have experienced.

Yea, I think it's just about time that I start working towards my Microsoft certifications.  I hope they will be enough to get me in to a larger corporate type position.

They usually are something that will get you to an interview. Depends how far you get along the track. There are others bebe careful about investing your time and energy in the wrong environment. Check out a few job adds in areas of work you are interested in and see what the requirements that they ask for are. You have to get the interview, once you are sat infront of the potential employer, you then have your chance to tell them all your skills etc that you have learnt this past 8 years, but it is the qualification that will get you there.

Obviously the MS stuff or Cisco stuff is the industry standard for general network support.

See the thing is that I do get the interviews without the certs.  The problem is that I go in unprepared for some of the questions they ask me.

I'm trying to find someone who has had a position like the following description who could help expand on the requirements and give me an idea of some of the types of questions I can expected to be asked during an interview for such a position.

Expert experience in VMware
Solid experience in supporting HP systems in a large scale Data Center environment
Windows Server Infrastructure
Provide system installation, maintenance, and support for all Windows based systems and services in a 3000+ server environment
7 years of experience building and supporting server hardware/software and MS Active Directory infrastructures in a large scale enterprise IT environment.
Firm understanding of Microsoft development tools and technologies and experience with Microsoft Operations Support process.
Possess exceptional problem solving skills.
Demonstrated ability to work in a fast paced, constantly changing team environment, as well as independently on complex technical projects.
Must be self-motivated, detail oriented and possess strong organizational and interpersonal skills.

For example, what exactly does "Expert in VMWare" mean?  I have played with vSphere in a test lab.  I know how to install and configure ESX and ESXi.  I know how to monitor performance and resource usage.  I know how to do updates, make backups, and use iSCSI for VM storage.  I haven't really had a chance to use vSphere with a couple thousand VMs.

Or as another example, what exactly does "Windows Server Infrastructure" entail?  I can create, configure and manage an Active Directory based network.  Map out Visio diagrams.  Create group policies.  Create users, groups, contacts, query based distribution groups.  I am comfortable with ADSIEdit.  I can ensure replication between domain controllers.  I can create and delegate control of child domains.   I can install configure and manage multiple Exchange versions.  Set up and configure Exchange clustering.  Use eseutil to repair Exchange databases.  Create VB and batch scripts to automate tasks.  Once again, I've done this all in small and medium sized offices, what could I be missing from my knowledge base that would make me unable to work in a 3000+ server environment?

Iyou write to some employers after your interview and rejection they will be kind enough to assist you wth why you did not get the job and may help you.
I would think it unlikely that anyone has all the experience required and therefore you would not be expected to be able to answer all of the questions and therefore a solid qualification would demonstrate a willingness to learn, a capacity to understand and confidence to suceed.

Well, I've already signed up for my Windows 7 70-680 course for later this week which will count towards getting my MCITP: Enterprise Administrator (Since both MCP and MCSE are outdated).  I know it is no replacement for experience, but I am confident enough with my skills that the training and studying will help me to better know how and where to fill in the gaps I have in experience due to the lack of working extensively in a large corporation...I really do wish I could find a weekly IT Pro bowling night or coffee meet-up or something so I can pick someone's brains.

Now that you mention it, I think going back into the consulting market and contract business would do me good, but I'm going to get my certs first.

This question could very well have been written by me.  I too work for a small business and have much IT knowledge and experience but have often been faced with the know-it-all nerd in an interview who feels obliged to overcome your, already, vulnerable disposition with highly technical and irrelevant questions.

I once answered "I don't know" to about seven consecutive questions in an interview then the fire-alarm went off - talk about "Saved by the bell".

One thing I have learned in seven years of interviews is that it isn't "What I know" but "Who I am" - nobody wants to employ somebody who knows all but cannot interact with other staff.  You have to imagine, if you were interviewing yourself, what would be my criteria - I can assure you that personality accounts for more than what you know.  Another important point to consider is that nobody knows everything, if they did, they would have a very boring IT career wouldn't they?

My point is this, work on yourself before your skills.  You can always answer something like "I would research the answer to this problem, resolve it, then make notes in my knowledge base so that the answer will be available should this issue reoccur"

Once you get that job, you can start working on your skills when they become relevant.  I learned a lot when I was doing my MCP, 90% of which has been forgotten because it just isn't relevant anymore!