About Folder Sharing

HI,
My users want to write data in a file through some application but when they access that file through network they can’t change anything on it.
So i created a folder in my server c: drive and given name financedata and provided all users write only access and shared that folder also.On sharing i have assigned only read only rights.But now when they access folder through network they can’t write anything but also they are also not able to write any data through application.I am using Windows 2000 for testing but i hv to transfer it to windows 2003.
Please tell me where I did wrong this is really urgent.
I would appreicate if someone could assist me.
Regards.
Anurag.