In a comment to my post here, Jim asked why he can't access the WSS object model in his code, even though it's running under the Sharepoint context. Since a month has passed and I can't re-enable comments on that post, I'll just answer here:
By default, the security settings for a Sharepoint site is set to WS_Minimal - a predefined set of security policies that can be found in C:\Program Files\Common Files\Microsoft Shared\web server extensions\60\CONFIG\wss_minimaltrust.config. You can change this to WSS_Medium to get a slightly higher security policy (that allows Object Model access, for one thing) or create your own set of security policies for exact customization. Check out the web.config settings in the SPS root directory to see how to define another ruleset, and use the existing .config files as a base.