To tweak it, go to
www.tweakfiles.com, and download the "Raid-On Tweaker". Just install the program, and there should be a BUNCH of options, and they will tell you what the options are. Also if you want to edit the registry without installing this, you could type in the following lines into your registry:
REGEDIT4
[HKEY_LOCAL_MACHINE\Software\ATI Technologies\Driver\0001\atidxhal]
"EnableWaitUntilIdxTriList2"="1"
"TableFogEnable"="1"
"WFogEnable"="0"
"ZFogEnable"="1"
"DisableHierarchicalZ"="1"
"DisableHyperZ"="0"
"FastZClearEnabled"="1"
"Vsync"="0"
"AntiAlias"="0"
"ZFormats"="15"
"ExportCompressedTex"="1"
"DitherAlpha"="1"
"ExportWBuffer"="0"