Computer

[Kreekakon]

First things first, you NEED a better CPU than that to be able to run anything at all. Pentium 4 is a single core CPU which means it is outdated by almost ten years. Although it sounds bad, an ATI 6450 is not the absolute worst thing you could come by (As in it can actually run modern stuff moderately well on very low), so I'd recommend you can stick with that.

I'll try to help you replace your CPU based on your motherboard:

Motherboard Name Gigabyte GA-945GCMX-S2 v6.6 (2 PCI, 1 PCI-E x4, 1 PCI-E x16, 2 DDR2 DIMM, Audio, Video, Gigabit LAN)

I did a bit of tinkering, and this came up:
http://www.gigabyte.com/products/product...x?pid=2521

According to the page, it luckily will support:

Supports Intel® Core™ 2 Extreme dual-core / Core™ 2 Duo / Pentium® D / Pentium® 4 / Celeron® D processors

So I'd recommend you go look for something from those series that is under $77.

Forget changing the graphics card, because $77 is not enough to make a worthwhile upgrade beyond the CPU, which according to your specs should be prioritized in replacement.