OK.. just installed OP in XP.. installed OP Enhancement Package v5.2 (coming soon, only had the updated scripts in it, if you have The Forge scripts installed, then you have v5.2 already) and it works perfectly for D2..
No issues in XP as of yet.. I did have to install all the device drivers for my system as my components are a lot newer than when XP MCE 2K5 came out.. but I just used Vista to DL the XP drivers, copied to the XP drive in the Documents folder, and restarted in XP, and loaded drivers.. NP at all.. system is zipping alone without a single issue so far.. but I am going to stress it for a week or 2 to confirm stability.
Vista users only have to get an XP install disk (preferrably Pro edition) and follow the guide and they can keep Vista on their systems and all their information and programs, and still install XP and it will work just fine...
I do recommend to not share program Files folders due to the way the Vista security is set up.. so that means install the software you want for XP in the XP environment, and Vista in Vista.. don't cross drives.
Hope this helps some Vista users out. This means that we can get some great pilots back on here if they still have an old XP install disk.