Are you sure there are no partitions on the second drive, only Linux? To make sure, open a terminal, become root ('su' command then your root password). Use
then press 'p'+enter and 'q'+enter to quit. You should see one (if your Linux uses /dev/hdb1 etc) or two partitions (if it's /dev/hdb5 or later).
If it's the only partition, backup all important data, then (again, as root) run
Parted has a text mode interface, the right command to resize your partition is 'resize'. You can also read help ('help resize').
The command will look this way:
resize 1 0 sizeofyourdrive