Freezing applications and claims of diminished disk space?

I am admittedly a little bit of a novice, so I apolgoze if this topic has already been thoroghly reviewed. Last week I updated my MacBook Pro to OS X Snow Leopard (currently running 10.6.8) and it has been running smoothly up until yesterday when I noticed applicatoins were freezing up, forcing me to restart in order to fix them. Once my computer restrarted it would run smoothly once again, for about an hour, until the probelm would reoccur.

Theoretically - my computer has plenty of free disk space and memory, however, sometimes if programs did not freeze I would recieve a message saying I was using too much disk space and had to close programs - trying to close programs from this prompt almost always results in a major slow down, or a never ending beach ball. I have been kepeing an eye on my activity log to try to monitor what could possibly be causing this sudden loss of disk space, but have yet to locate a viable culrprit. I've done some internet searches and become aware of the term "memory leak" - is this problem I am expierencing?

Using the disk utility I have verified and repaired permissions, which seems to offer a temporary fix, but in due time the programs begin acting up again and once again I am forced to either force quit applicatoins, or restart.

Something else I've noticed is strange behavior with web browsers - I have both Safari and Firefox. If FIrefox freezes up and I force quit the program and then try to reopen it, it will tell me that "A copy of Firefox" is already running (this "copy" of FIrefox does not show up in the acitvity log.) If I force quit Safari and reopen it will refuse to connect to specific websites (most notably Facebook and these very Apple communities.)

I think that is all the pertinent information - I am mostly curious if this is something I can fix myself and how I would safely go about doing so.

Thank you.