GET RID OF THAT VID CARD!!!!
IF you have A PCIe slot, get a 6800, or even a 8500GT.
The 6800's are going for about $60 US, while the 8500, with DX10, is going for $79 US.
But, you are right about the processor, get a "real" pentium.
You are certainly in a fix;
The broadband will help...A LOT
A new processor will help...A LOT
A new Vid card will help...A LOT
In the end, tho If you don't mind playing at low rez (which you probably already are
I would go with the broadband first.