Fox Wildung

mmm, i noticed that my SL have problems with shadows aswell, maybe someone is able to help me with that problem I have a ASUS G73JH (Republic for Gamers Notebook) with following specifications: OS: Windows 7 Ultimate 64-Bit Version (Build 7601) CPU: Intel i7 Q720 1.6GHz Memory: 8 GB RAMM GPU: ATI Radeon HD 5870 Mobility 1GB Catalyst: 12.1 I'm able to play SL on fully settings, but as soon as i turn on shadows, then i lag badly and i have no clue how to fix that with kind regards Fox Wildung