I'm searching for a developer with good skills in EMC Documentum, WCMS, VMWARE

I will recommend you to install your VM using RedHat or SUSE this will give you a flexible development environment, it will also allow you to install different versions in the same box. I will also recommend you to set at least 3 GB of swap and use at least 2 GB of RAM. If you are brave enough and don't have RedHat or SUSE licensing try Fedora, I was able to install DCTM 5.3 SP5 and DCTM 6 SP1 without a trouble. Of course you will have to use Oracle, here is a link that can help you install Oracle on Fedora:

http://www.oracle-base.com/articles/10g/OracleDB10gR2InstallationOnFedora7.php

You can also try Sun VirtualBox instead of VMWare, it is free and has the same functionality than VMWare.

Note that RHEL isn't freely available, but CentOS is the de facto replacement. If you're not familiar with CentOS, it's as closest to RHEL as possible sans the branding. You can find plenty of CentOS VMWare applications freely available online.

When selecting an OS, keep in mind that certain applications (including databases) are only certified on specific OSs.

I'll also note that VMware and DCTM are both owned by EMC. I haven't used VirtualBox with DCTM, but developers have been using VMware for years.

To Rsuliv1...

This is the main question...  As you say, "EMC does not make DCTM software available to the public."
On the other end they do not let you enroll in a partner program easily even if you pay for it.

Some time ago, we wanted to know more about Oracle... we have registered to their website, download the DB 10g... we have trained on it, and finally bought it for our production application.
In the case of Documentum, it is not possible. On the other end, when you buy a licence, they tell you that you can duplicate it on as many test environment in your labs...  Will I finally find myself spending 40k¬ for a licence i'm not sure to use ?
Plus, they are not sure they can sell the 5.2 or 5.3 version to me... And it is the one i'd like to use at start...
We do want to start dealing with this product, and then when a client wants to go to this kind of solution, suggest Documentum, sell the licences, and integrate it, and provide them a good service...  But it seems they are not interested by this scenario.
Do I definitely have to switch to sharepoint ?

If you want something you can lay your hands on try Alfresco (http://www.alfresco.com/), it is open source, it is free and it was founded by one of the former Documentum engineers.

Correct, Oracle's OTN offers a free membership allowing you to dev their software, which is great. When Stellent was Stellent, opposed to Oracle UCM, they allowed for a temp license for development. I'm not sure if DCTM allows for this type of temp license. I doubt it as the software itself isn't time-based.

If you're looking to become a VAR of DCTM, you're best bet is to purchase a company license for development purposes or partner up with a consulting firm that already has access. Again, you'd have to call one of their sales staff to see if they can make any better arrangements. If you can provide immediate client needs, perhaps they can work something out for you.

Regarding 5.3 vs 6.x, I know that 5.3 is the standard version that most clients are using, but they are quickly moving to 6.5. 6.5 has been available for about a year and has enough general buy-in to make people comfortable with adopting.

If you are a VAR looking to get into the DCTM realm, then your options are limited. On the other hand, if you are shopping for ECM solutions, there are other enterprise-level solutions out there. Oracle & Alfresco are options, but I'd be very weary of Alfresco. I can say that v2.2 was very very buggy and didn't allow for simple customization at all (e.g., extending the object model requires Spring bean extension & a restart of the app server; having to restart the server for configurations in a prod environment isn't practical, but i read that they were looking to fix this by implementing dynamic-types or something like this in v3.0 or later). Alfresco also doesn't have the add-ons that DCTM & UCM offer. But, if you're very familiar with the dozen or so open source frameworks (e.g., spring, jsf, hibernate, etc) the ramp up shouldn't be too bad.