Did you mean Ti4800? If so, the Ti4800 is a decent card. Equivalent to the TTi4200 which was a good all rounder a few years back.
120GB is plenty enough. It depends on what you going to use the PC for really. If your going to be downloading and storing loads and loads of files etc then the bigger the hard drive the better. I've had my PC for 5 years now and i'm still struggling to fill up 40GB! lol.
You got a pretty decent system there and i'd be happy to have that as my main system.
The mainbord only cost £35 anyway, When I wanted too enqure about the cases they had in the shop where I brought it I told this guy I wanted a case too Support an AMD Athlon XP too my suprise when I got it home it was a case for a pentuim 4!! Maybe I should sell this case and get a 300watt case instead!!
You could buy a case and psu separately. Most builders would reccommend that as the quality of the psu tends to much better that way. Poor quality PSUs are frequently the cause of erratic or failing computers! Any ATX case should fit any ATX board whether it's 'intel' or 'AMD'. Now you've got the case, just buy another PSU, that's my advice :)