Installing Windows 7 64 Bit On A Dell 8400 Running Out Of Time?

I have a Dell 8400 and a few questions about upgrading to Win 7 64 bit. (I am a complete NoOb when it comes to installing an OS).

First my specs are...

CPU Type
Intel Pentium 4 HT 630, 3000 MHz (15 x 200)
Instruction Setx86, x86-64, MMX, SSE, SSE2, SSE3
L1 Trace Cache12K Instructions

[Code]....

I will have 2GB of this RAM Thursday with another 2GB of the same RAM the following week or the week after that. Corsair Dominator DDR2 Ram Memory PC-6400 800 MHZ [URL] After the RAM I will be getting a new Graphics Card. Also I have a spare 650 watt PSU if needed.

I ran the Window upgrade advisor and the only things it flagged was (of course) that I only had 512MB of RAM and outlook express. It did say custom installation required, whatever that means.

1. My first question to everyone is, can my Dell even run Windows 7 64-bit?
I googled around and it seems possible.

2. My second question is can I install it with the 512MB of RAM I have now?

3. My last question is can I install this along side XP on my HD?

4. My third question is does anyone know of a good very detailed step by step Noob guide for installing it next to XP?

I have never installed an OS before and if it does not work I am screwed!

I do know it is better to do a fresh install and no I cannot by another HD right now, I know they are cheap but I will be scraping together all I have just for the RAM and Graphics card.

My problem is that, I really only have the time to do this over the long weekend and cannot wait for the RAM to get here.
The guy on e-bay is a clown and did not ship it when he was supposed to and it will not be here in time.

I just need it up and running and can add the RAM as it comes but I am under a serious time constraint and if I don't get this done now over the Memorial day weekend it will be a long time before I have enough time to do this.