I have a 2.8 GHz Core 2 Duo, 2 GB Ram, Running 10.5.7.
The problem I'm having, some applications ie Firefox and iTunes are very slow starting or Not Responding, when browsing, I get the beach ball when scrolling up or down pages with the mouse wheel. Actually the beach ball came up 3 times while typing this. Is there something I can try or should I buy some sort of System Utilities Software to scan my drive for errors?
Thank you for you help in advance.

Well, assuming all of your software is up to date... You could try Maintenance3.8 (http://www.apple.com/downloads/macosx/automator/maintenance.html) Available from Apple - Downloads.
It is an applescript that I use regularly. Normally I select every option except for "Clear Cache Files" You can read about what each option does more specifically in the "read me" file. Maintenance Repairs Permissions, Verifies Preferences, Update's Prebindings, does a Periodic Clean-up, Cleans the Cache, Updates Locate, Whatis, LaunchServices Databases, Rebuilds Spotlight Index, and it will keep a log to show you what it found wrong and fixed. I've never had any issues with my mac, software-wise, and I think Maintenance had a lot to do with it! It is worth a shot anyways even if it doesn't fix your problem.

My machine was doing the same about 2 months ago, it was my hard drive. It failed a short week later. Replaced my hard drive and restored from the last time machine backup and everything was good to go. Back to normal. I put in a 7200 rpm 500gb seagate and the system runs great.

Make sure you are backed up NOW

How big is your drive???

How full is your drive??

Check SMART Status in Disc Utility - you must click on the drive icon NOT the volume icon.

My machine was doing the same about 2 months ago, it was my hard drive. It failed a short week later. Replaced my hard drive and restored from the last time machine backup and everything was good to go. Back to normal. I put in a 7200 rpm 500gb seagate and the system runs great.

Same here. It's started happening when I did the firmware upgrade about a week ago, and died yesterday. It's currently at apple having the drive swapped out. If you haven't already, back up the drive now. Good luck!

My brand new as of 2 weeks ago MBP has been doing similar. Firefox or Safari, when watching flash based video sparks it the most often. A couple days ago I had it happen when setting up for recording my band, and All that was running was ProTools. I am going to try formatting/using the reinstall DVDs, and see if it keeps happening. If it does, I guess calling apple is the next step.

Is there a way I can restore the system to a couple weeks ago before I got 10.5.7 update with Time Machine I have 206 GB available... of 296 GB The 10.5.7 update is when all this started to happen.

Do I enter Time Machine/select system and restore?