yeah allmost every program will work on Windows XP x64, as it has a emulation on board to run all the 32bit versionb of program...
but there are very few option for AntiVirus... but in this days few major AVS company does came up with 64bit AVS, such as KAV 6.0 will work... AGV will work..
but few small tools which may be important to u, may not work in Windows XP x64, i have seen with my system...