A quick peek on eBay for 512MB PC133 modules says that some can be had for $15 shipped using Buy-It-Now. So for $30, less if you get lucky on auctions or find a pair like this one: http://www.ebay.com/itm/300740305034
($25), you can max out the memory at 1GB. That should improve your system's speed a little bit but as you note, video will still be a significant bottleneck.
Some things which you can do to speed things up without spending any $$$:
- defrag the hard drive
- consider changing browsers
- consider changing antivirus program
- examine what processes are running in the background and terminate those you don't need
Despite the T23 being one of my favorite systems, I actually haven't been using one for several months. Both home and work systems are now being covered by A31p. It wasn't anything to do with the speed or responsiveness; I simply needed the extra screen real estate (UXGA vs. SXGA+) for an application I've been using.