So if you are having problems programming for Sharepoint 2003, then here is some help.
First to you need to reference Microsoft.SharePoint.dll. You should be able to do most of what you need using this dll. Now if you cannot find this dll on your box you must retrieve it from the server with Sharepoint installed. Using the command prompt, access the GAC and copy the file to where you can access it.
Now if you get the error below:
Preparing resources...
Updating references...
The dependency 'Microsoft.SharePoint.Security' could not be found.
The dependency 'Microsoft.SharePoint.Dsp' could not be found.
The dependency 'Microsoft.SharePoint.Library' could not be found.
Performing main compilation...
Building satellite assemblies...
Then you are most likely developing on a remote box. So here is the issue, you cannot run code of from a remote machine. The code must run on the Sharepoint server. After thinking for a bit, it seems reasonable that you would not want remote code running around your Sharepoint sites, especially if it was exposed to the Internet. So you must run code that references the Sharepoint dlls directly on the box with Sharepoint installed. So you may be asking but i need to use Sharepoint API functionality from a remote box, the answer here is create a web service to service your needs.
Hope this helps and save you a lot of frustration.