I think there will be a difference in performance, but I don't think it'll be a huge one. AMD is better for gaming than intel, but the intel youi choose is more powerful than the amd you have.
I don't know much about GeCube vid cards, but it has the same basic chipset as your old one. You might not get a huge performance increase from the vid card.
If you are gonna get intel, then I would suggest getting a socket 775 motherboard and cpu. It'll give you better performance and is newer technology. The only problem with 775 is that it's a little pricey.
Intel E6750...........PSN: ELBATROP
XFX nForce 650i Ultra
Patriot PC2-6400 8GB (4x2GB)
36GB WD Raptor
Samsung SyncMaster 931c
Samsung SyncMaster 750s
Windows 7 Home Premium 64