I've seen comments posted about the playability of Aces High and how it's too strong for many older machines.
I have a 3 or 4 year old Dell Dimension 4550, nothing stellar, and I was having issues with screen stutters and freezes. I spent $50 on a graphics card from Ebay, Radeon 9250, mid range at best, probably less, and $100 to upgrade my 512k system mem to 1024k and now it's smooth as silk all issues are gone. Being able to load textures into memory makes a huge diff.
Since my initial $50 graphics card investment, I'm considering upgrading again just to see what I get out of it. I've got all the video options enabled and running at a high resolution.
So my point is, some cheap upgrades to your system will probably cure your ills, no need to get a new system, AH2 is still kind to a wide range of CPU's. If I could only upgrade my ACM and gunnery skills at BestBuy life would be perfect.