i'm afraid not. the PSP is compatible with DUO media which is half the size of regular "memory stick" format media.
for example, a MEMORY STICK DUO or MEMORY STICK PRO DUO will work with a PSP while MEMORY STICK and MEMORY STICK PRO (or ULTRA) will not work/fit because of it's size.
however, there is a product you can buy called the A.R.M. Memory Stick Jacket. it's sort of a passthrough device to convert a memory stick duo slot into a memory stick slot. this will leave you with a large appendage hooked up to your PSP which will diminish the sleek look it's know for. in short, it's not pretty but it works. this is possible because MS and MS DUO media have basically the same electric interface. only the connectors and size are different.
i should point out that the media speed will also play a factor in compatibility. i don't want to induce you into error so i will only tell you to do your research but i've heard reports that the higher-speed memory sticks will not work with the PSP. memory stick duo and memory stick pro duo are confirmed to work and i do believe that memory stick pro duo high-speed also work but i have no idea about the other ones.
