There is still a lively emulation scene for the commodore 64 and a number of emulators still being updated for new windows builds.

CCS64 V3 and up (current version is CCS64 V3.4) will emulate the c64 perfectly under windows xp using direct x 9 and can be found here

For many other platforms (including handhelds) one of the best c 64 emulators available is frodo.