Last year Hardocp reviewd the XPS Gen 2 (same as m170 except name) with the 6800Go Ultra
HERE. They compared it to the 6800 Go
HERE. Numbers tell the story. Both cards have the same features - the difference is in type of memory used and far greater GPU & memory speeds. In fact, the 6800 Go Ultra is exactly like a 6800GS, which is roughly equal to 6800GT/Ultra.
My m170 runs older games (HL2, Far Cry, Doom3, Quake4, etc) at 1920x1200, 1680x1050, or 1600x1200 fine for me. Call of Duty 2 needs to run at 1440x900 with details maxed out or higher res with textures set to "high" instead of "extra". BTW, Prey demo runs great at 1600x1200.
If your 9300 has the base LCD (1440x900, I think) the 6800 Go will probably work OK. If you have the TrueLife LCD (1920x1200) and want to run at max or close to max res, you'll need the Ultra. I believe you might be able to stick a 7800GTX Go module in there also. That is an upgrade path for the m170, and the physical chassis of both m170 and 9300 are the same. The only issue would be the power supply & adapter. IIRC the base 9300 has 90 watts, where the m170 has 135 watts. Also, my LCD panel seems to scale lower resolutions pretty good in games, but regular text can be pretty fuzzy.
There are laptops where video can be replaced - my old Inspiron 8200 had replaceable modules built in. Dell is not alone in this - higher tier/boutique lappys have upgradeable GPUs also.
I didn't find any Go modules at Dell. You can call them and find out availability/pricing. Ebay might also help.