The real-time portion of anti-virus programs try to intercept, read and scan everything being read from or written to disk. This can cause problems with any program that is trying to read or write a lot of data, particularly install programs and games. That said, if you don't have a problem leaving an anti-virus program enabled, there is no reason to disable it. The clean re-install description assumes there was some problem, so eliminating all non-essential background programs is the safest way to re-install the game, since it eliminates one potential source of problems.
I once tried installing the drivers and default software for a sound card on a computer someone else had installed an anti-virus program on (which I didn't notice at first). The install was very slow, and eventually just locked up the computer. After rebooting and disabling the anti-virus, the install proceeded normally.


The Starforce copy protection is required by the game, and will be automatically re-installed if it is removed. You could try a manual update, which might provide newer drivers than those included with the last patch. However, I would expect copy protection problems to effect all saves pretty much equally.
Updating or removing StarForce drivers


If you say yes to the imp historian he should put the teleporter stone directly into your hero's inventory (miscellaneous section, most likely on the left side near the category tabs, if there is room there). Try saying no; in that case he should drop the pyramid on the ground.
Check the secondary skill menu (icon by the portrait) for your characters; after the imp leaves there should be a couple new icons, one to use a teleporter and the other to drop and use one.