My 4 GB microSD card only allows me to use 1 GB

I hope this is your phone, from that page I came to know that your phone has the Symbian OS. I hope there's an option in those phones to password-protect a memory card.

Nokia E5-00 - Memory card security(Though it is for a different model, I hope it also applies for your phone too.)
If I recall correctly, if you password protect a Memory Card in those phones, pc does not recognise them. But, if you put the Card in another phone which support Memory card password protection, then you can access the memory card, but only after entering the password.
If you remember the password, you may put it in another phone which support the option, enter the password, then remove password protection from your card. Thereafter you can access it from your pc. On the other hand, if you do not remember the passwor, put the memory card to the phone where it works, remove the password (I remember that the option is in the gallery->click option on memorycard.).
If you can't do both of them (how sad, isn't it), put it in another phone that supports password protection and format the memorycard.

Disc management (Windows) or disks (Debian and derivatives) will show you the usable space. There are also command-line utilities diskpart (Windows interactive program: use list disk) and sudo fdisk -l (Linux) to show the same information.

If you format it with full sector checking, this will confirm that the whole space is accessible.