Regarding your new processor, you say you do not have DDR ram, well being perfectly honest (whilst trying not to sound like I'm a little rich geek)
I would buy a new motherboard that supports DDR and get some DDR memory.

a basic (but very good) motherboard would be a motherboard such as a:
Abit VA-20 Micro ATX (Socket A) Motherboard - £38.00 Including Vat
(this supports upto 400mhz fsb so u could go upto a 3200+ Athlon)
or
Asus A7V600-X (Socket A) Motherboard - £36 Including Vat
(also supports 400mhz fsb, Onboard 6 channel Dolby sound card, onboard 10/100mbps network card and supports Raid - again you could upgrade to 3200+)

Memory wise:
GeIL 512MB (2x256MB) PC3200 Value Dual Channel Kit CAS2.5 = £57 Includnig Vat
Or
Corsair 512MB DDR Value Select PC3200 CAS3.0 Kit = £59 Including Vat

I suggest you get PC3200 memory (if u go for a new board) as it runs at 400mhz max (without overclocking) so you could run a 200mhz FSB cpu (ie: 3000+ or 3200+ Athlon XP CPU's.

Hope this helps