Yes it will. The only thing that MIGHTcause you problems would be a high-end graphics card; say a Radeon 1650/1900/1950, or an NVidia 7300 or above. As it is, you didn't say, but from your question, running 1 HDD, 1 DVD/CD drive and any normal video card, even a high end card, will work fine with 300 watts.
MCP, MCDST, HDA, CSS
(I guess that would qualify as a computer expert)
PS- I am running an AMD Athlon 64 3800+, TWO DVD/CD burners, TWO hard drives, a Creative X-fi Extrememusic sound card, NVidia 6800/256mb, 1.5 gb RAM, all with a 400w power supply-I think you'll be fine.