Easiest way is to start again.
Run windows setup from the CD and when it finds the partitions delete them and reinstall on to the full 80G drive.
If the hard drive or partition has a previous installation of XP you want to remove, choose to delete the partition by pressing "D". You will then be prompted to create a new partition in the empty space. This will remove all data from the deleted space.
If setup returns a message the partition contains the setup files and cannot be deleted use the info from this link: Delete NON-DOS Partition click here
10c If you intend to use multiple partitions, or dual boot, this is where you specify the size of the boot partition and or setup location for XP. If you are planning to dual boot XP, I would create a small 100 meg DOS partition for the first primary partition, then an 8 to 10 gig partition for XP. You can partition and format the remaining space after XP is setup from Disk Manager. If you do not intend to dual boot, you can either use all the un-partitioned space, or create an 8 to 10 gig partition for XP and leave the rest free to partition later.