Gentoo swap not used.
 

Me and a friend have a gentoo linux box.
we use it for mail server, webhosting etc.
sometimes I upload big files to that server (its in my local network) then i look at my phpinfo to see how many disk space i have left.
now what bothers me is that it used 99% of my ram and 0% swap space.
does anyone know a solution to let gentoo use the swap space?

AFAIK the use of swap is totally automatical. If the system can function normally without using swap, it will do that. System will only use swap when needed.
Also, keep in mind that that 99% use of RAM includes the cached and buffered ram, so that 99% is normal.

and when i upload to my server its going at a speed of 1 mpbs (when i upload to another windows system it goes at an average of 5mbps). so i thought uploading to my server went slow because of the 99% use of ram. and when my upload is done, the ram stays at 99%. why is that?

Linux manages ram way different from windows. Linux will always optimize your ram by using it caching and buffering files, taht's why you always have 99% used ram. When more ram is needed, Linux is freeing cached ram.
File transfers is not a process eating ram (AFAIK). I never had more used ram because I was transfering files with an ftp program, so I think the reason of that slowness is due to other things.

Because linux uses RAM aggresively. It doesn't free up memory right away like windows. It just caches things until another app needs the space. Its actually more efficient.

I don't know why uploading to the linux server is 5 times slower then uploading to the windows server. What do you have running on the linux server? What kind of disks do you have?

Slower disks equal slower writing time which could make it look like your network is slow.

I have apache running on my linux box, it has 2 7200 rpm 80 gb drives and the type = "xfs"