I'm using Windows XP Professional exclusively on all my PCs, so SW2006 is in a folder named "SolidWorks 2006" and SW2005 was in a folder named "SolidWorks 2005". When I first installed 2006, I left 2005 in place so 2006 could discover anything it would out of 2005 to carry over as many of my customizations as possible.
Now that 2006 seems to have been running fine for some time, I went ahead and uninstalled 2005 and deleted its folder in Program Files on my home PC. If all goes well, I'll be doing the same on my work PC soon.
Thanks!
Tim