Currently in the midst of updating XP Pro 64 bit on Dell Optiplex 740. Has been successfully activated & registered to Microsoft with my information.
Don't see the need of wasting 4GB of RAM with the 32 bit version (out of 8GB), so went with the 64 bit. So far, so good. It's a business computer anyway, and XP uses considerable less resources than Vista Business that I just formatted over.
Microsoft posted before the cutoff date of support that XP could still be installed, activated & all updates through April 8, 2014 installed. The monthly MRT Tool is available every month through July 2015 & I highly recommend to open it & run a Full scan with the app, the one performed after install is a short scan. One way of running it is downloading a fresh copy & selecting Full Scan. This is the silent "scrub" tool that MS gives to all supported Windows users each month.
The other, and simple way (I just verified it), is to click Start, then Run & type "mrt.exe" (w/out the quotes) in the space. This brings up the MRT interface, and a Full scan can be ran. Note that this process can take a long time on some computers.
So yes, as long as it's a legit install, fresh or re-installs of XP are fine. This is also a good time to create a backup, once it's fully updated, to have a clean XP install on demand, when needed.
EDIT: Speccy specs of fresh XP Pro 64 bit install below:
Edited by cat1092, 18 November 2014 - 11:08 AM.