Like GG, I've been using Win 7 since the Beta came out. i was so impressed with it that I fitted a second hard drive in my laptop so I could boot either. I've not used XP Pro since.
Win7 is very clever at updating drivers and the like, and finding drivers for all sorts of hardware. I've been seriously impressed! But it's not deleted or even messed with anything on either machine. I've not heard of it doing so.
The only problem I've had (and it was serious at the time) was when I deleted the Windows homegroup that I never use. That resulted in it locking up the hard drives on BOTH my desktop and the laptop. I could start the machine, but I was told I didn't have the right to access anything on either machine.
It turned out MS knew about the problem, but didn't have a "fix". The only cure is to install Win7 again (on a spare partition if you have one), then boot to the new installation, and use the admin privileges to change the "owner" of the locked-out hard drives back to "Administrator" from the long string of numbers the Homegroup delete changes them to.
After that, you have two bootable and useable installations of Win 7. EasyBCD will allow setting the "main" one to default start, and all is well again.
But in none of that did any software or other stuff go walkabout.