Hey Bud
Well, what i would do is i would make the query to contain all the records, as ianatkin wrote, then i would look at the response it gave, the reason you get other records could be related to the os name is written in another way, (you can get that if you have installed other clients, dagent/aclient).
If you take ian's post, you should get all your records. :)
And to answer your question regarding dbo.computer, yes that is the main table, if your computer isn't in that table, it's not there. :)
After you tried the above thing, you could try andy's post, in a slight edited way.
Use eXpress
SELECT name
FROM dbo.computer
WHERE (os LIKE '%XP%')
Kind Regards
Morten Leth