Memory Suggestions for Asus P4C800 Deluxe or P4C800-E Deluxe

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I'm currently in the process of building a new machine and need some suggestions / input reguarding which memory module{s} to purchase. I am trying to achieve a multi-media / gaming machine. I plan on using a Asus P4C800 Deluxe or P4C800-E Deluxe MB {Haven't made final decision yet}, a P4 3GHz 800MHz FSB processor, ATI All-In-Wonder 9800 Pro {128MB} vid card, Creative Labs Sound Blaster Audigy 2 Platinum sound card, Sony’s Internal DVD±RW Drive DRU510A, {2} WD 120Gig HD's w/ 8M Buffer, and either 2000 Pro or XP Pro for a OS. I'm trying to put together a good system that will be expandable / versatile on somewhat of a budget. I am a advanced user but only a novice when it comes to overclocking and tweaking machines to their limits. My memory budget is what is getting cut into. I originally planned on starting this system out w/ 2Gigs of memory, but that's not happening. So, my question is this: What module{s} should I purchase to start this system off with? I'm not sure if I'll be going with 1Gig of memory, or 512MB of memory to start off with. So I guess I need both scenarios {what mod{s} to purchase if i only get 512MB and what mod{s} if I get 1Gig} keeping in mind that I will double my initial starting memory within 6 months.

Thanks
-Good ideas in need of some advanced knowledge-