System very slow after a few hours

Hello. I have Suse 8.0 with kde3 and my sytem is very fast (PIII 850MHz with 320Mo of RAM and a swap about 260Mo ) at boot time but become very slow after a few hours. With procman i get a root task kdm X using about 77 Mo memory after booting, but about 300Mo after a few hours. What can i do about that? I know at my swap is not optimum but i was having much less RAM when i have installed the system and i have not yet the oportunity to reinstall it with a bigger swap. I think at the problem is the RAM usage, because the kdm X process is using it (about 300Mo on 320 after a few hours) . Is it possible to clean this RAM ? Even if i close all the programs except kdm and procman the memory usage of kdm X is not going down.