Well, first thing I'd try is booting into SAFE MODE with NETWORKING. See if it is still slow there. If it isn't, then 'assume' something you normally start is the culprit.
In that case, click on start and search for MSCONFIG.EXE. Run it at look at the STARTUP TAB. See something you do not expect or know there, un-check it. Re-boot and see if it is OK. Otherwise, consider doing a CLEAN BOOT :
To perform a clean boot on a computer that is running Windows Vista, follow the VISTA steps from this MS KB article.
Hopefully after this it will be fast. Now start turning on just the services and check, then a few STARTUP items at a time. Eventually you should be able to narrow down and even identify the problem area or determine you have none.
Irv