You should be asking how many times have you installed or reinstalled if not repair installed XP. I lost count between my own and other systems people had there!
For 7 let's now... the 32bit 7000 so far saw saw the intitial installation replaced to see the XP/7 dual boot since the first was over to the XP drive while booted in Vista at the time. 2 there plus the unlocked 32/64 Home Premium each only 1. The 64bit Ultimate 7000 saw 2 with a second on an ide drive added in later to see 7068 replace that now unplugged leaving a grand total there of "5"! for the 7000.
The 7068 did see a second install with the first going on the present stand alone for the x86 7077 while the ide was still in use. 7068 x64 wasn't still trying to get online with the x64 7000. 7068=2
One each for the 7077! As a general rule I rarely have to wipe a drive once a clean install is seen in working shape. Vista has seen about 5 total since it came out from swapping drives(ide to sata) along with one repair install back in 2007! Even that sees a better track record then XP!