This might be ugly but it should work. Map the pc from the run prompt by typing "\\PCNAME\c$" less the quotations, where PCNAME = whatever name is assigned to the PC for which you are trying to see who is logged in. That should take you right to the root of the c: drive. From there you can drill down to the documents and settings folder which will list all the users who have logged onto that PC along with the date and time. Sort by date modified and see who the last user to logon was.
I'm sure there is an easier way that perhaps someone with more knowledge than myself can provide to you but that should get you what you need ugly as it is hehe.
"Once you can accept the universe as matter expanding into nothing that is something, wearing stripes with plaid comes easy"
Albert Einstein