My acer laptop has 160 gig memory but i can only use 80 how do i make it all available

Download and run the GParted live cd.
Burn this on a cd and boot from it.
this will allow you to view all partitions on the drive including those that are hidden or unformatted. This will also allow you to change the partition size without degrading content, FIRST DEFRAG THE DRIVE.

Gparted will allow you to format the space(other 80 gig) as ntfs,FAT, or linux ext.

There may be other partition managers that are free, I'm just familiar with LINUX. Plus if you want to fool around with a small linux distro that runs entirely from ram, download PUPPY Live cd.

Most likely, your partitions are simply sized wrong. If you have Windows Vista go to:
Control Panel>System and Maintenance>Administrative Tools>Computer Management

In Computer Management look at the list on the left and click on storage and go to Disk Management and look to see if the entire disk is partitioned. I will talk about what to do if there are two partitions in a moment, but for now, lets assume that you have an 80GB Windows partition and around 70GB of empty space.

Right click on the Windows partition and click expand and simply follow the instructions in the Wizard.

Now, lets say there is a partition sitting there. Most likely, if it's there, you're using it without noticing that you are. Make sure there is nothing on it. If the partition is empty, right click and delete it and follow the instructions I provided above.

Now, if you have Windows XP... well I'll just wait for your feedback because this explanation is even longer.