For playing latest games i recommend using bootcamp instead of Parallels. The 3dmark06 benchmarks on my machine (early 2011 15'' Macbook pro, Radeon 6750M, using latest parallels and vmware fusion) speaks for themselves (rounded to fifties):
	Code:
	Version      Mode              Version          Score    Performance
Windows 7    Bootcamp          Catalyst 11.11   9600     100%
Windows 7    Parallels Desktop 7.0.15052        7550      79%
Windows 7    VmWare Fusion     4.1.1            6550      68%
Windows XP   Parallels Desktop 7.0.15052        5300      55%
Windows XP   VmWare Fusion     4.1.1            5550      58%
 All machines was set to 3GB ram and 2 cores. Graphics settings was on max.
NOTE: Windows XP cant use more than 256MB GPU RAM that is the reason why it scores so low.
NOTE2: Also, this table does not represent the performance on NVidia GPU's, on NVidia this may be completely different.