CPU upgrade?

I just got the game Portal, and my PC can barely run it on low settings. At first I thought the problem was in my graphics card, which is rather low end (it's a GeForce 7300LE), but when I checked the performance tab of Task Manager I realized that my processor, a Pentium D 915 (2.8 ghz) was maxed out while playing the game. I have 2 gigs of RAM, and they were only at about 60%, so I don't think that that's the problem.

Anyway, I don't trust myself to decide whether the processor I'm looking at (Core 2 Duo E7400) is compatible with my motherboard, and even if it is, if it will offer a significant improvement.

My motherboard is a Dell 0WG864 (at least according to CPU-Z). Both processors use 775 LGA, but one is 65 nm and one is 45 nm, I don't know if this makes a difference as I really don't know anything about CPUs...

Any help would be greatly appreciated. I can answer any questions as needed.

The problem isnt with your processor, it is your graphics card. portal is based on the source engine and doesnt need much power to run. I'd suggest picking up a radeon HD 4650 for around $70 and the game will play fine.

yes. I believe the 9600gt would be a better comparison to the HD 4650.

no, a 9600 is about the same speed as a 4670 and slightly faster than the 4650.

yeah, I'm pretty sure a low end card like the 9400gt wouldnt be able to take advantage of that extra memory anyways.

Thanks everyone. If for some reason this doesn't fix it I'll be back.

either one should be fine

you know i put the 9400GT in my computer and it made a big difference on gameing graphics i have the same computer as you do the 7300le is a bad card for the newer games that are out now and the 9400gt runs on the low 305 watt power supply the dell e520 has but if your looking to upfrade your prosseor still you can upgrade to a intel core 2 quad q6600 as long as you upgrade to the latest bios it dosent make a big proformance upgrade thoe unless your running vista it seems to be made more for it hope this helps you out