I know those are the official numbers, but they aren't always accurate. I'm just saying since the newer one supports 8GB, it's very possible that the previous one does too since their hardware is extremely similar. The cap on ram is a motherboard issue, pretty sure at least, so if they changed the motherboard in the tx2z (which i have no clue how different that one is), then there's the difference, and the reason why the tx2500z won't support 8GB. As far as upgrading past 4GB, i'd say just stick with 4GB. I got 2x2GB sticks for $39 from newegg, and one 4GB stick is $170 from them (for ddr2-800). I'm using windows 7 32-bit with a 2GB paging file, so I have 2.8GB ram total (2813MB, for some reason it's not ~3300MB minus 256 for the graphics), and it runs fine. You can disable the paging file if you don't run anything memory intensive like photoshop or games, and don't keep a lot of tabs open in internet browsers. I'd recommend just having at least a 512MB paging file anyway.