Want to increase spead and reponsiveness in older Mac Current Information:
Software:  Mac OSX (10.5.8)
Processor:  2.4GHz Intel Core 2 Duo
Memory:  1 GB 800 MHz DDR2 SDRAM

I want to get my computer moving faster, specifically around safari, itunes, iphoto, etc. Would it be easier to just erase my entire Hard Drive (backed up of course) and buy Lion (10.7) or Mountain Lion (10.8) since I would have to upgrade to snow leopard (10.6) before upgrading to Mountain Lion anyway?  Trying to be cost effective and keeping it simple and not compounding the issue of responsiveness and freezes.
Upgrading to Lion or Mountain Lion would not improve your Mac's performance. It may actually decrease performance as the newer versions of Mac OS X seem to require/want more RAM to run smoothly. Apple has increased the minimum amount of RAM in almost all of their line up to deal with this issue.

You currently only have 1GB of RAM... upgrading this would probably be the cheapest and most efficient method of speeding up your Mac. Freezing and unresponsiveness can be caused by lack of RAM. 

Check out this Apple support article that will teach you how to use OS X's Activity Monitor to check whether RAM would improve performance.

After determining whether or not you need more RAM (you do!), you can find out what kind by following these steps:


Click the  in the Menu Bar
Click "About This Mac"
Click "More Info..." in the About This Mac dialog box
Click on the "Memory" tab


Listed will be what type of memory you have and how much. In the lower right hand corner is a link to "Memory Upgrade Instructions" — follow these instructions.