I'm cleaning up a Windows XP PC for a friend and I found 2 processes running on startup.
SQL Server VSS Writer
DeviceVM Meta Data Export Service
What are they needed for and is it save to disable them?
I have no idea what the 2nd is but the first allows backup services to request SQL server to put the SQL database in to a state that will give a clean backup (no half written transactions and whatnot) so the backup software can get a copy of the database files.
If you have that service you have SQL server installed, if you are running full system backups you will need it to reduce the risk of bad data in your backups but you don't "have" to have it running if you stop it.
However on the other hand instead of guessing what makes your computer slow to start up and guessing which services you can blindly shut off, measure it! (note that a lot of these tools where developed for Vista or newer, but some still work on XP in a limited fashon.)