As the XP-90C weighs in at 690g without a fan it exceeds the Intel recommendations for max weight of heatsink (from what I remember) - so technically no, it's not compatible with ANY mobo!!
However, ignoring that... I found this on the Thermalright click here website...
'With a customized LGA 775 adapter kit, XP-90 can be installed on a Intel Pentium 4 socket T motherboard. So far, we have not found any board that is not compatible with XP-90. (Some Asus socket T motherboards such as ASUS P5AD2 Premium may have mechanical issues due to Stack Cool module on back of motherboards. Please check with Thermalright resellers for new version LGA 775 adapter kit before you place your order.) We would appreciate if you could report them to here'.
From the reviews I've seen I thought that the XP-90C came with the LG775 bracket now (the XP-90 does not), but this site seems to suggest otherwise... may be worth checking with whoever you buy it from first.
In my (humble) opinion you may be better off with the aluminium XP-90 (I use one of these with my AMD64 3500, with a 92mm Vantec fan) - it's only about 2C hotter than the copper version, and is much lighter.
Or the current cream of the crop for HSF's is the Akasa AK913 - currently the 'Elite' recommendation for HSF's in Custom PC magazine.