my 1GB card was only able to hold 600MB or so of files at first. turns out it was in RAW format, formatted the card in pc using fat32 solved the problem.
As others have suggested, you might want to format the card to get to the full limit of the card.
A FAT16 file system (most likely what you will have your card) has the following limits:
1) Root directory is generally limited to 512 entries.
2) Other directories are limited to approx 2^16 entries.
3) The entire volume is limited to approx 2GB (4GB on some systems like XP).