Your Elements is a PowerPC binary if it's not version 6 that was just released a couple of days ago. Although the latest versions of Tiger took care of many of the Rosetta problems, it still suffers from substantial memory leaks in addition to being a memory hog. Thus, those PowerPC apps that use it will still suffer somewhat. I think your first purchase should be an upgrade to Elements 6. Second purchase would be 2 gigs of RAM. Don't get any more than that (two 1 gig sticks) as it won't work in your computer. If you have a single 1 gig stick (instead of two 512 mb sticks), all you need to purchase is another 1 gig stick (about $25).
Watch
this video and buy either a 2.5" USB enclosure with a SATA interface or one of
these do-dahs (they are great - I use mine all the time). Before replacing your hard drive, use
Carbon Copy Cloner to clone your internal drive to your new drive attached to the USB port via the do-dah. Then all you have to do is pull your old drive and install the new one. Only takes 10 minutes to replace the drive and install your new memory.
That's the beauty of CCC - you will not notice anything different about your hard drive - other than it'll have a lot more space on it.
It will be an exact clone of your hard drive. If you buy a 2.5" enclosure, you can put your old drive in it and use it as an external drive.