Connecting to an existing Server Farm

You need to use a "magic string" for the SSEE database - \\.\pipe\mssql$microsoft##ssee
Also, you need to enable access to the database from external sources - see this article http://channel9.msdn.com/forums/TechOff/255490-How-to-connect-MICROSOFTSSEE/ 

Sorry, it should be \\.\pipe\MSSQL$MICROSOFT##SSEE\sql\query

if you have a stand alone setup then by default you can't add another server to the farm. And if you are using the windows internal database then I'm not sure why you would even need another front end as a single front end will have much more capacity than that database does

sharepointguru14 is correct, in that you can't connect another server to a default install of WSS 3.0 (reference: http://technet.microsoft.com/en-us/library/cc287960.aspx see "There is no direct upgrade from a stand-alone installation to a farm installation"
However, I'm not sure what he/she meant by a single front end as having enough capacity?  You wouldn't add another front end server for capacity/storage, you would add it to load balance/fault tolerance or help balance throughput/performance or both.
Here is your options:
1. Do nothing, you have the WID, unlimited size, live with a single front-end server
2. Install SQL Server Express and now limit yourself with a 4.0GB database size (free SQL, get what you pay for) and then create a new farm (see below) as the WID only comes with a standalone WSS install (the unlimited free SQL)
3. Bring online a full SQL Server (2005, 2008, etc.) or attach to an existing one by creating a new farm
For options 2 and 3, your steps would be (there is much more to it, but this is high level):
1. Create a new SharePoint farm (on new server?) choosing Advanced and connect to a real/full SQL Server
2. Install any custom templates, webparts, features, etc.
3. Get a site collection backup from the old server
4. Restore a site collection backup to the new server (new web application)
5. On your original SharePoint server, disconnect from the farm
6. Connect to the new farm that can scale out
For your Site Collection backup and restore, use this procedure I wrote up: http://blog.brainlitter.com/archive/2009/03/09/how-to-refresh-a-sharepoint-sandbox-collection-with-production.aspx but instead of having Production and a Sandbox, you'll instead have "Old Production and New Production" - backup from one, restore to the other (new farm)
Hope that helps.

by capacity I don't mean storage. I mean load balanced, front end activities. With the windows internal database you are running everything on the same server. So adding another frontend provies you better "farm" capacity in the sense that you will have more CPU, memory, and throughput to process requests. Why I say it doesn't make sense from a performance standpoint is because you 1. aren't going to get any HA or fault tollerance since you still have a single point of failure with your DB server (which happens to be the most important one) Then a WFE will handle many more requests per second then the Windows Interal DB will and now you would have 2 handling requests. The free windows db is still going to slow you down. If you were going from a standalone install and you want to make your farm better and more reliable functional then the first place money should be spent is putting it into a SQL server preferrably a clustered setup.

But if you have a extra server and were going to do a 2 server farm a stand alone SQL server should be 1 server and everything else on the second. That will give you the best performance, throughput, capacity, etc then any other config for 2 servers.

hope this helps

Can I say under stand-alone installation, I have no way to attach additional web front-end as I cannot "touch" the database remotely. And if I want to do this, I have to upgrade database from internal database to sql server?

Thanks itgroove and sharepointguru. On sharepoint farm design...could u please give me some examples on good architecture?...I originally want to deploy multiple web front-ends and each of them connect to a seperate database instance (I will use sql server 2000), for the sake of easily managing and having clear design, but no load-balance solution will be used. any comments?

sorry to add additional question.

I have read a simiar article from Microsoft - http://technet.microsoft.com/en-us/library/cc288334.aspx
Thank you for your information.