1664 megs of ram, what dimms did you put in to get that freaky number?
Anyway stop fretting about inactive memory, if you arent using any swap it doesnt matter, also look at the number of apaches or inactive processes you are running, more likely than not these are responsible for your inactive memory. But in any case inactive memory isnt bad for the system, it means nothing unless you are heavy in swap usage.
49 processes: 2 running, 47 sleeping
CPU states: 10.1% user, 0.0% nice, 15.5% system, 0.0% interrupt, 74.3% idle
Mem: 167M Active, 559M Inact, 123M Wired, 580K Cache, 199M Buf, 1159M Free
Swap: 512M Total, 512M Free