Is this normal memory usage for LR3.5

I'm noticing that despite moving up to a computer with double the ram (still an older computer), I'm actually getting a less responsive experience. This is most noticeable when I'm exporting RAWs (from a canon 5d classic to large jpegs). During the export lightroom is mostly unusable due to lag--I'm cool with that. What bothers me is that when minimized, I can see major lag in even the way my mouse cursor scrolls around. Is this what I should expect from my rather crappy system ?

Also: if LR is bringing my computer to its knees, why isn't it at least using all the RAM is can first ? I never see it use more than about 1gb. Why not 2gb ? Moreover--why is it using ANY virtual memory if it hasn't even depleted the RAM ?

thanks for any suggestions.

Lightroom version: 3.5 [775451]
Operating system: Windows 7 Business Edition
Version: 6.1 [7601]
Application architecture: x64
System architecture: x64
Physical processor count: 2
Processor speed: 2.8 GHz
Built-in memory: 4094.5 MB
Real memory available to Lightroom: 4094.5 MB
Real memory used by Lightroom: 981.7 MB (23.9%)
Virtual memory used by Lightroom: 1076.4 MB
Memory cache size: 414.3 MB
System DPI setting: 120 DPI
Desktop composition enabled: Yes
Displays: 1) 1920x1080

LR4.2 works fine with me with 4Gb, you just may have a lot of software running in the background

Plus you haven't said what hard drive (spindle speed would be helpful) you are using or the what type of processor like i3, i5 or i7 or if indeed it is an AMD cpu