Don't go to Vista yet. Period.
My parents just bought a Dell Dimension with Vista Home Premium, and although the interface is awesome, the core OS is buggy. Many games crash regularly, and some applications fail to launch after installation. Jedi Academy installs and plays, but once you close it, it will not open back up unless you open it from the autorun menu. Speaking of autorun, any time you insert a CD, open a network place, or try to copy files, it will ANNOYINGLY darken screen and ask you "Do you wish to allow <program> to perform <action>?" NO DUH! OF COURSE! Why did I drag the files and say Copy in the first place? Vista is just stupid, and until they fix the bugs, stick with good ol' XP.
...Or use Ubuntu Linux, but that's up to you