Hmmmmmm..... I've never installed anything that way. (never had to, i use XP)
Only thing i can sugest now is System Restore. That will re-set your system to an earlier date (which you have to pick, there is usually a restore checkpoint once or twice a month added by the computer by default).
Just make sure you set your system back to a date earilier than the one when you installed the demo. Take it back to a date 3 months ago or something. That should get rid of it.
Start>All Programs>Accessories>System Tools>Syestem Restore. It will ask you whether you want to create a restore point or choose one. Select the latter then press Next, then select the date of the restore piont you want to go back to; take it back 2-3 months or so and select a date. It will ask you if you want to proceed, select Yes, it will show you the restore piont, when you click continue, it will restore.
And that should be it.
If that doesn't work, then i'm out of ideas.