A hand-pump to serve your beer without gas? You're going to be disappointed! Although you will probably find using gas doesn't mean you can't enjoy your beer as "cask conditioned" unlike what CAMRA will try to tell you.
When you pull beer out of the cask you need to replace the "void" you are creating with sterile gas (CO2) or else do as the pubs must do and get the entire cask drunk within a very few days. If you just allow air in the remaining beer will start going off in a matter of days. CAMRA will tell you this how it must be, but unless you have a bunch of very thirsty friends your health will suffer repeatedly trying to drink an entire keg before it turns! Remember CAMRA look after the public visiting pubs, they don't look after home-brewers!
Pubs try to get around this by using "breathers" which replaces the "void" with CO2 but at zero pressure. You can do this. Your beer wont go off, but it will go flat! Hand-pumped beer isn't flat, it contains almost 1 volume of CO2 dissolved during fermentation for starters. "Breathers" do allow this dissolved CO2 to slowly disperse and the beer suffers. Doesn't have to happen in pubs because they turn over the beer quickly.
Another option is to use a "check-valve". It isn't a check-valve at all, probably got that name in a lame attempt to put CAMRA followers off the scent. It's a "demand-valve". Your beer is kept under pressure (about 3-8PSI) and only opens the valve when the hand-pump attempts to pull beer. Without it the beer would just pour out of the hand-pump! It's a cheat, but one that allows us home-brewers to use hand-pumps.
The next big issue is how do you get a CO2 regulator to work at 3-8PSI? You do need to keep the pressure low or your beer "force-carbonates" (I can tell its happening at about 4PSI, CAMRA tells you it will happen if a CO2 cylinder just comes within the same building as the beer!). Not as easy as it might appear. I do it by "modifying" air-brush regulators; I know Dads_Ale uses a more involved system with an "intermediary" vessel at zero pressure (CAMRA might even approve).
Long-winded post, but I wish I could have found this information when I first wanted a hand-pump!