Substantial upgrade - Windows reinstall required?

I am about to upgrade the following components of my system:

- Motherboard from Asus AV7266-E to MSI K8N NEO2 Platinum
- CPU from Athlon 1900+ to Athlon 64 3500+
- Graphics card from Geforce Ti 4600 (Gainward 750 XP) to Gigabyte NVIDIA Fanless 6800 128MB AGP

Will I need to reinstall Windows XP?
Am I likely to have problems with activation?
Would you recommend a reformat of the C: partition?

There seem to be widely differing views about whether to reformat or not, so I should very much appreciate reasons.
Thanks

The computer probably wont even boot into Windows if you dont do a re-install because the old chipset drivers will try to load. Ive tried several times and its never worked. Its best to backup your data or move it to another partition and format your primary partition, C, and do a clean install. I keep all my important data and downloads on a seperate partition so I dont have to worry about loosing anything when Windows craps out or I have to re-install. You shouldnt have a problem activating Windows as long as you have a valid product key.