We have a server at a friends house with a hard disk that's filling up so he picked up another hard drive.

My question is.. can I install it and then configure it so to the user it seems transparent and they just see the extra space all on one drive/directory? (From Windows)

It's running centos 5 with samba ... with EXT3.. and I don't believe it's using LVM.

Without lvm it's not going to be seamless, I'd suggest looking at the way space is currently being used and identify part of the directory structure to highways to the new drive. You'd then just gourmet the new drive as ext3 are what you like and going it in a temp location, e.g. /mnt. Then copy the chosen directory onto the new file system. Once that's done, mont it over the top of the chosen dir and test it out. Once you're happy you can then temp un mont it, delete the old copy of the files and mount it again. Job done, very safely.

btrfs offers this facility - one command. Works well on the several machines I use it on. All non-production it must be said - but it's just about ready. Production admins should be anal about backups anyway ....

Doesn't help you for ext3 - do as Chris suggested.

The easiest way is just to mount the drive as a subdirectory of your current drive. While it may not be contiguous it will seem just like any other sub directory. I actually use a separate drive for my /home partion this way.

Thanks a lot guys.