i'm going to move mye disks to another computer, they are configured with 2 disks in RAID1 and 4 disk in a LVM group, as i am moving these i will reinstall the OS (debian sarge) and was wondering if my LVM and RAID configuration will remain or do i have reformat the disks ?

If you are reinstalling your OS, you will need to reconfigure both if it is new hardware as well. Unless this is hardware raid and you take the controller with you to the new machine, it will require a reconfiguration. And LVM is configured on the OS level, so it would need to get reconfigured as well.

it's software raid, but when i reconfigure, will i lose any data?

The only way to not lose data is if you were migrating the disks attached to a hardware raid controller and moved to similiar hardware without reloading the OS. What makes you think you wouldn't lose a software raid configuration if you planned to reload the OS? The answer is yes, reload the OS, you will lose the configuration and any other files you don't have backed up.

Yep, trickykid is right.
Your best option is to backup all the data, except for the os. Load your new OS, then copy your backup files to the new OS.
I know, depending on how much data you have, that is easier said than done.

i think im gonna cry, it's 600gb

That's nothing. I had to deal with backing up over 80TB of data at my last job.. with over 500TB of total backup space usage on tape..

Another option would be to buy new disks. Build the new system and network your old system to the new. Then you can use the old system primarily for backing up theh current live system. Sure better than most tape backups.

There is also Tank drives that plug in via usb. Not sure how expensive they are but being so portable makes them perfect for your task.

True since it's only 600GB but tape backups are varied upon the scale of data being backed up. The tapes and drives I used could backup 600GB in a matter of hours, actually if nothing else running, they claim to max at 80MB a second write to tape.

But yeah, 600GB is not that much but if you truly have 600GB of data you don't want to lose, best case is to get some more disks and copy over. But ask yourself, do you just have 600GB total or is this 600GB filled up with data? How much of it is OS data that is installed during the install.. and how much is configuration and files you don't want to lose? That plays a key part in what you actually backup, reinstall and reconfigure/restore old data.