I'm all out on ideas. If it works in 32bit XP it should work in 64bit, dual boot or not. Also, generic drivers should work unless hercules implemented something special that prevents windows from using generic (ones from ralink site) drivers. Hercules drivers are from 2007., so I doubt that they'd include Vista64 drivers and not XP64. Nowadays most hardware has same drivers for XP and Vista, graphics card and motherboard drivers are one of exceptions. I.e. drivers are the same as in file sense, but "they know" what part to use when installed on XP, and what on Vista (same was for 32bit, only one set of 32bit files inside).

Last thing I can think is to try with these drivers, I hope it's OK to post rapidshare link

rapidshare.com/files/144144476/RT2500V3.0.4.0_WinXPx64.zip

These are the drivers I used with XP64 year or so ago, they are older, but my card worked with these. These are pure drivers, no control panel or anything, just drivers, zip is around 120 kb in size. You need to install them manually. Right click on wifi card in Device Manager, Update driver option and then browse to folder where you unpacked it manually. If windows say they can't find compatible drivers for your hardware then hercules must have implemented something that prevents windows to use the card with generic drivers.
Funny thing is, I found on more than one place that it says card supports XP64 bit, like here www.touslesdrivers.com/index.php, and drivers on that page are the same as the ones from hercules site (HWGPCI-54-V3.1.exe).