I found the manual was enough to get me through upgrading and moding my tc4200 =). just keep an eye on your screws and stuff. I found removing the plastic under the screen swivel to the be the suckiest part cause you can pop keyboard keys off if your not careful. if you lay the screen out as flat as possible it comes out easier. putting it back on though takes some finesse.
wouldnt bother going to 2 gigs since the chipset on this tablet doesnt support dual channel. but if you have a 512mb version, the 512mb is in the internal slot under the kb, so you can add a 1gb stick from the underside without having to take anything appart.
the harddrive is no problem, just make sure you get a IDE one. the tc4400 and most new laptops have SATA but the 4200 is IDE.
im running the stock 740 with a shot of arctic silver on it, 1.5 gb of ram and the stock 40gb drive. system is zippy under xp. i modded mine for airflow though cause when in tablet mode, the screen covers the only inlet for the fan. not a noob mod though, cause it involved a complete dissassembly of the tablet heh.