Most likely already known but if you link up to a .txt file on your memory stick through the web browser your PSP then you'll be able to view the file, essentially making it simple to view text on your PSP.
(If you make web pages (.htm and .html) these will work as well, as can clearly be seen by the various portals available)
Also typing in the link address of a animated .gif on your memory stick through the browser will allow you to view the animation (Stupidly the animations do not load when you view the pics from the XMB)
Links to your memory stick work like this=
(you have to put .filetype otherwise it won't work)