Windows:

Windows XP (32 or 64 Bit), SP2
Windows Vista (32 Bit or 64 Bit), SP1
Windows 7 (32 Bit or 64 Bit)
Windows 2000, SP4 and Update Rollup 1

RAM:

Min. 256 MB RAM (Windows 2000, Windows XP)
Min. 1024 MB RAM (Windows Vista, Windows 7)

HDD:

Min. 150 MB (additional temporary and quarantine space needed)

Note:
Administrator rights are required for installation under Windows. Windows 2000 won't be supported any longer as of 13 July 2011.