yeah i have Half Life 2 and those specs will run it fine on a good res. yeah the graphics card isnt great but the scalibility in game is good enough that this wont be a problem.
the most important spec there is your broadband because, as you may or may not know Half Life 2
requires Steam and a Internet connection to run. Although Valve say that Steam will work on 56k i have read on the Steam forums at
www.steampowered.com which is the official site that people using 56k have had a highly unsatisfactory experience with the authentication process and the general use of Steam. you may have also heard that you can run Steam in offline mode and while this is in theory true in practice many people have to sign in due to error and bugs and so must connect to the internet.
without knowing whether you plan to buy the steam or retail version it is hard to tell what kind of experience you should expect. please post this info.