There may be a problem with your fstab. So, boot up using a Live CD like KNOPPIX
, and from there browse to your partition's /etc/fstab file. Open that up in a text editor, and you should see a line like this among any others:
/dev/hda3 / ext3 defaults 1 1
If it is different to that, try changing it to the above line - that may help solve the problem (defaults includes rw).