Hard Disk upgrade

I currently run a shuttle ak31v3 board, xp1700, 512 Mb pc2100 MEM with
1 DVD rom and 1 CD reWriter 16x Cyberdrive and 2 80 Gb Drives IBM,Maxtor

I am thinking of replacing the writer with a DVD re-writer Liteon 811s
and a new hard drive as the others are full :(

Questions:

Adding another hard drive to my current system means a new controller card so I thought a new motherboard with sata connectors would be a better idea

thoughts on the Asus A7V600-X VIA KT600 £47.39 at ebuyer

Next a new hard drive: speed or space

Western Digital 36.7Gb 'Raptor' £88.14 or 160Gb 7200 sata drive

Will I notice a speed increase in windows and applications with the raptor or is it just not worth the cost

Lastly feel free to recommend alternatives and best places to buy from thanks