New rig and memory question

[banja]

Please forgive my ignorance, I'm not very knowledgeable about system upgrades etc.

I want to build a new PC later this year. With the very low prices of AMD chips and boards, I would consider building a system around a 939/ AMD 4000 config, but I'd like to perhaps upgrade later to Conroe (spring next year). Will I be able to use the DDDR2 memory that Conroe will require for my stopgap AMD system?

Ideally I want to only replace the CPU and mobo when the time arises. Or will I have to use seperate memory types for both systems?

Thanks in advance

 

[banja]

Thanks. I'm wondering whether it would be better to last a little longer with the system I have, and then go straight to conroe.

Thanks for your answer

 

[banja]

XP Barton 2500 @ 3000
ABIT NF7-S
ti-4200
1gig PC3200
80 gig HDD

There's nothing I really want to salvage from this system. Everything from the PSU to the HDD will need to be upgraded, so I figure I can sell this system on as it is.

I may get a GFX upgrade just to last me a few months, as the 4200 is seriously lacking now (Prey demo was 10fps!) which I could later sell seperately, or leave in the machine to increase it's sell on value.

Another idea was Asrock dual mobo as my stopgap (with AMD 4000+), which I could put my newer AGP card into.

Going for a whole new Conroe system is going to cost me about £700, which I won't have before Christmas.