Good Upgrade + GPU Suggestion?

I'm planning to upgrade my socket 478 Pentium 4, and I've put together a new motherboard, CPU and RAM set (will purchase all separately; works out cheaper). Would you all consider this a good upgrade? Or should I purchase an Intel processor/socket? Will I be able to connect to a HD TV, and a PC monitor? Also, will I be able to play games such as Call of Duty: Black Ops? I don't intend to play many games, but I would like to be able to run a few; whenever I have time away from Uni.

ASRock N68C-S UCC, on Socket AM2/AM3@ 1000 MHz FSB (2.0 GT/s)
AMD Athlon II X2 215 @ 2.7GHz (Dual-Core)
8192MB (8GB) DDR3 Memory, PC3-12800 1600MHz

The cost will total to £92 (Great Britain Pound). Of course, that does not include a graphics card. Would you please be able to suggest me one? I am looking to play few games, and am NOT looking for SLI/CrossFire (to keep costs low - motherboard doesn't support it either). The most demanding game which I may play will probably be GTA: IV. Also, I will probably upgrade the CPU at a later date; when I gather more funds (so don't worry about bottlenecking, haha).

Would you say it's a good upgrade for £92? Also, my current computer as specified below (for comparison sake, of how much of a difference in upgrade):

ASRock P4i45GV R5.0 motherboard, on Socket 478 @ 533/400FSB
Intel® Pentium™ 4® with Hyper-Threading, 3.06GHz @ 3.4GHz (S-Spec: SL6PG) - Single-core
2048MB (2GB) DDR1 Memory
NVIDIA GeForce 6800 GPU with 128MB video memory

Since I will be upgraded the motherboard, CPU, RAM, and graphics card; all the rest will stay the same - the hard drives, case, psu etc. Therefore, I'm wondering whether my current PSU is adequate to power the upgraded components. My current PSU is 300-watts.

All the questions again briefly:
- Worth the upgrade for £92? If not, please state why (thank you).
- Could you please suggest me a GPU to play games with; nothing too expensive (i.e. £100)
- Is a 300-watt PSU adequate to power the upgrade? The computer has 3 HDDs, 1 DVD-ROM, and 2 case fans (once upgraded, I'll only attach 2 HDDs).

Thank you for reading all this, and I appreciate all your responses. Thank you very much!