I have a laptop (/w XP) and whenever i attach an external hard drive, xp mounts it as ready only. This happens only external hard drives and not for thumb drives. when other people log into the same machine they are able to read/write to the external hard drives. also when i log in to other machines i am able to read/write as well. its only with this machine and my id that i am not able to write. i have played with permissions a lot and its not that for sure (because it happens in all the HDs). i think it might have to do something with registry entries.
I think that you should create a test user to verify this. Once the test user can connect to the drives then you will know that you will have to recreate your windows profile.
Here a very good illustration on what you need to do:
Be sure to backup as necessary.