Windows 7: AMD M860G with ATI Mobility Radeon 4100 custom aspect ratios

First off here are my specs:

Toshiba Satellite L505D-LS5010
Windows 7 Home Premium 64-bit
AMD Athlon II Dual-Core M300 2.00GHz
4GB RAM
AMD M860G with ATI Mobility Radeon 4100



Here's my issue: I'm playing Sonic Generations (via steam) and I know I'm under the minimum specs but it seems to run okay at lower resolutions like 800x600 and 640x480, but the image is stretched vertically. Someone on another forum suggested setting up custom widescreen resolutions like 640x360 or 800x450 to fix this and linked me to this application: software « Morrisoft
He said it worked for Sonic Generations on his computer so I tried it.
I entered 0800x0450x60 and 0640x0360x60, clicked the "save table" button and got this error message: http://i.imgur.com/Z1qDP.png
I clicked "details" and this is what came up: exception - Pastebin.com
It was also recommended that I edit the registry manually, following these instructions: How to Add Custom Resolution to ATI | eHow.com
So I edited it manually like so: http://i.imgur.com/Gvpb4.png
I then rebooted my computer, booted up Steam, selected "Sonic Generations" then "configure". The new resolutions didn't show up in the list, so reselected my graphics adapter by clicking here: http://i.imgur.com/PiLKC.png
And I get another unhandled exception message: http://i.imgur.com/C1vDt.png
The details are here: exception2 - Pastebin.com
I tried multiple times and even hit "continue" at the unhandled exception notices (probably a bad idea) but I think I may have inadvertently made things worse. What should I do?