Buying a new PC will I see a noticeable difference in speed?

I haven't had a new computer since '04 and my current one just got a virus and I thought it would be a good time to get a new one. My old specs are XP Pro 64bit, Amd Athlon 643500+, 2GB Ram, and a Radeon 1800 XL... New one I am looking at specs are Vista Home Premium 64bit, AMD Phenom X4 9100e(1.8GHz), 4GB Ram, and I am going to throw my current graphics card in there. Will I notice a difference in preformance mainly processing speed?

What is your budget?

As a tip buy a good CPU, good Motherboard, and a good Power Supply, these 3 components are most important.

Looking at the config you stated you would see a very significant jump in performance 2x better I'd say (possibly 2-4x better cpu wise), but I would heavily recommend downloading and installing Windows 7 RC, and pre-ordering Windows 7 Home Premium as your OS from Amazon or wherever is still doing the cheap pre-orders.

I see you prefer AMD CPU's, I would go for a higher clocked Phenom II X2/X4, 4gb ddr3 ram (OCZ are good imo), a good 790 chipset motherboard like Gigabyte GA-MA790XT-UD4P, and a Ati HD 4850 512mb gpu (recommended upgrade), a power supply company that most recommend is corsair especially their TX and HX series.