Just a few queries:
1 - while your mobo supports 1gb RAM, what about your BIOS version - does it need upgrading?
2 - are you sure that you have the correct RAM? If you got it via Crucial's online selector, then contact them and you can return it if it is not suitable.
3 - does the new chip work ok alone - i.e. without the old one in?
4 - what is your mobo manufacturer / bios versions? - some mobos do have RAM issues.