@ChuckFinley, they have on board SSD. There was a limited model (701 SD) which had a slot under the access panel to add an additional SSD to up the storage but i was never able to find one so had to settle for the 4G.
As for the performance its hard to say, you have to remember that the processor only runs at 633MHz single core, and RAM makes a difference. However, there is a few Linux scripts available to allow overclocking of the processor but i found that the fan started having a fit when i did, which resulted in using another script to control the fan speed but once set at 100% the battery life went south very quickly.
If you really would like to use this machine, i would suggest reading up on Arch but only looking at DWM with dmenu, or an openbox setup (DWM if you have a fair bit of linux experience and command line / Openbox if you would prefer a application menu via right-click). Dont try to get too fancy with it, its an old piece of harware but it can be used for simple functions. I would check with the hardware however via a live distribution on USB to check and see if you have the 2Gb or 4Gb SSD version. I am using 1.9G (55%) with my limited but functional Arch install.
Otherwise, your choices will be limited to older out-of-date eeePC specific distros which will still be functional to an extent, but may be a little harder to find on the intarweb