FreeBSD not giving back memory

[edward]

Hi all,
I use 5.4 Stable on an i386 machine with xorg 6.8.2 and kde 3.4.0. I 
have been doing a number of RAM intensive tasks such as converting video 
files and moving big files (7 or 8 Gb) back and forth over a LAN. I have 
also installed and configured Wine, although I haven't done much with it 
just yet. I have 26 Gb on my FreeBSD partition (excluding swap) that is 
used up at 78%.
I notice that when quitting all applications, the RAM used is not 
released and 476 Mb of RAM out of 512 Mb available are still indicated 
as being in use. Is FreeBSD not giving back memory when processes are over ?
Edward