so i tried playing prototype on my pc today and even though it lags like an old biddy on a zimmer, i can tell its awesome. My question is can anyone give me some pointers on upgrading cheaply so that i can run new games at least on lowest settings without lag>?
Here is my specs: (i know its messy but i dont care

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geforce 7300gs
Windows XP Professional Service Pack 3 (build 2600)
Enclosure Type: Desktop
1.80 gigahertz AMD Sempron
128 kilobyte primary memory cache
256 kilobyte secondary memory cache
Board: ALiveNF6G-VSTA
Bus Clock: 200 megahertz
BIOS: American Megatrends Inc. P2.20 12/07/2007
278.08 Gigabytes Usable Hard Drive Capacity
78.66 Gigabytes Hard Drive Free Space
PIONEER DVD-RW DVR-112D [CD-ROM drive]
VUTWX R0X2FWL6RS SCSI CdRom Device [CD-ROM drive]
3.5" format removeable media [Floppy drive]
ST3120020A [Hard drive] (118.06 GB) -- drive 0
ST3160815AS [Hard drive] (160.04 GB) -- drive 1
2048 Megabytes Installed Memory
Slot 'DIMM0' has 1024 MB
Slot 'DIMM1' has 1024 MB
Slot 'DIMM2' is Empty
Slot 'DIMM3' is Empty
Local Drive Volumes
c: (NTFS on drive 0) 118.05 GB 10.91 GB free
d: (NTFS on drive 1) 160.03 GB 67.75 GB free