Yes RAM's speed can bottleneck a system though it is not common because generally the slowest RAM you can get won't do it. Your RAM is 800MHz as the 400 is multiplied my 2 sine its "Double Data Rate". This is the standard ram speed for DDR2 and is fine.
Your RAMs speed will not bottleneck your system, neither will the amount you have (3GB).
I have DDR3 that says 1333MhZ on packaging. (2gig x2=2666Mhz?) Does that make my 3.1 Ghz processor useless?
My CPU is never full capacity (its max frequency usually hits the ceiling) in performance monitor. The cpu is 3.1ghz Athlon II, with 4g 1.3ghz DDR3, a 7970 amd, and 6gb/s SSD why do I still have loading screens?