I have an old Toshiba Satellite that I have labeled as my "Poker Laptop" and it runs good with PT3 running and 4 tabling on PS.
Processor: 1GHZ Celeron Coppermine (Plan on installing a 1.0 GHZ Pentium III for better performance.)
RAM: 512MB (looking for 1GB 100MHZ to test) Documentation says it only takes 512MB but I have found some other info that says 1GB will work.)
Before I run PT3 and my poker client I stop all items that are running in the background that I do not need which includes my firewall and Norton antivirus. These are turned back on when accessing the web.
I have also optimized the laptop using the MajorGeeks site which I highly recommend. You can push a little bit more performance out of your laptop or PC.
http://forums.majorgeeks.com/forumdisplay.php?f=48Search for laptop or whatever operating system you are using tweaks on your favorite search engine.
So basically I just wanted to let everyone know that PT3 will run with minimal issues on an older system. You might just need to optimize or find yourself a 'poker only laptop'. :) Good luck!!!