Right I just had a look at your system's specs. Assuming it is a Vaio PCV-R528DS 500 MHz Intel Pentium III. By Sony 528 is this what you meant?
If it is then...
Memory
You most likely have 128 MB SDRAM (perhaps just a single module). Exact type can vary but I expect it supports 100 MHz but critically it'll be a 168-pin DIMM. Now your new Soyo board most likely only has has 184-pin DDR SDRAM sockets so you're going to have to buy some new memory.
Video
Probably a ATI Rage 128GL with 16 Mbytes SDRAM @ 125 MHz. I could be wrong but I think this should work fine in the AGP slot of your new board.
Sound
You probably have on-board sound - with no separate PCI card. If this is true then you'll need a new sound card.
If you are buying a new hard drive why not just do what you suggest - a clean install on that. Then assuming everything is working nicely - plug in the old drive as a secondary drive and copy across all the file you need to the new drive. Of course you'll need to reinstall all your software on the new drive.