Making the most of a 300w PSU

Hello,
I've been searching the forums on scores of sites looking for someone with my specific problem. I just want to know if I can replace my 45w CPU with an 89w one without overloading my power source. I bought a budget Dell Inspiron 546 last year and now I want to max it out without replacing anything intensive (motherboard, PSU, CPU cooling.) Here are my current specs:

Dell Inspiron 546
300w PSU
320GB 7200rpm SATA Hard Drive
2.8ghz Athlon le-1660
780G AM2-based motherboard
2GB 800mhz DDR2 (2 Dimms)
Gigabyte Radeon HD 4550 (128mb DDR3 w/Hypermemory)
USB mouse, keyboard, and webcam

I am dead-set on replacing my weak video card with an HD 5670, which draws 62w max. I want to know if my PSU can handle another 44w on top of that (upgrading the single-core athlon le-1660 to a dual-core athlon x2 5800+. And also if the stock CPU cooling fan can handle the heat (I do not overclock.) If not I think I'll get either an athlon x2 5400+ (65w) or even an athlon x2 5050e (45w).

Thanks!
 
So even though I'll effectively be adding over 100w to the load, I shouldn't have problems with the PSU being overloaded?

Also is there a big difference between the 2.6ghz 5050e and the 3.0ghz 5800+? I am planning on doing some gaming. Aiming for High settings and 60fps at 1024x768 resolution. On pretty much every game I can get my hands on.