Help max out my memory/CPU

I have a Dell E520 (yuck) running a P4 and 1GB of DDR2@533. I am looking to upgrade both. The motherboard has its limitations though...I can run up to 4GB of 800MHz DDR2 (4GB in single channel 400 or 2GB in dual channel 800). The FSB is 1066MHz. I am planning to get an E6600 Conroe CPU (2.4GHz, 1066 FSB, 4MB cache). Also, I am running Windows XP. I have 2 questions:

1) Is it worth it to get a CPU with a 1066MHz FSB when my ram can only run to 800MHz? I could save money by getting an Allendale CPU @800MHz FSB.

2) Should I run my memory as 2GB 800MHz or as 4GB 400MHz?

I may be making this more difficult than it is. Please help!

1) Your fsb is actually only at 266mhz, and the ram is only at 400mhz. You don't need to downgrade to an allendale because the ram is already bottlenecking the cpu.

2) If you only have XP, I'd say go with 2gb of ram instead of 4.