My HDD has some bad sectors, should I be getting rid of it?

I have a 500GB SATA HD (not sure on model, if you really need to know tell me and I'll open the case), and it has some bad sectors on it. It also seems to be getting slower too. I haven't defraged it for a while (6 months or so), and its pretty full, so that may account for the slow. There are some files on it I can't delete as well. So is this thing dying or will it probably be ok for a while?

edit to add: Unfortunately this is the HD that has my windows install on it, it's on a seperate partition, but if the drives failing I'll just bite the bullet and upgrade to windows7 as I'm on xp right now and I'll have to clean install 7 anyway, just gotta get a new drive, unless you all think the thing is fine. I just spent a bunch on upgrades so I hate to have to spend MORE on the stupid computer, but I'll do what I gotta do to keep the thing running....

Drives cannot remap bad sectors if they are unreadable; you need to write to them so the drive knows the "old data" is not needed anymore and its willing to remap the bad sector and swap it with a reserve one.

If you download HDTune and check the SMART values, you can see Reallocated Sector Count, but also the number of "pending" sectors. If this value is not 0, you need to zero-write the HDD; this will make the value of pending sectors go to 0 and the Reallocated Sector Count to rise. In this case the drive has succesfully remapped the bad sector.

Formatting will not zero-write the HDD; you may do this with several utilities, best are some on the Ultimate Boot CD or simply a Linux livecd (like Ubuntu) and perform a command like this:

!! DANGEROUS !! Destroys all data on the target drive. USE WITH CARE!

sudo dd if=/dev/zero of=/dev/sda bs=1M

This command will write zeroes to the entire drive named /dev/sda. Disconnect any drive except the drive that needs to be zero-written so you cannot make a mistake with the drive name. Disconnect any USB sticks/external drives; etc. The command is case-sensitive. Double check before you hit enter.

Software or operating systems normally cannot see the bad sectors. Only for very old harddrives were the bad sectors truely visible and FAT/NTFS kept a list of the bad sectors which they simply avoided. Nowadays, the harddrive hides the bad sectors from the operating system/software by simply replacing them with a reserve sector.

But... this cannot happen if the bad sector is so badly damaged it cannot be read - swapping a bad sector for a reserve one requires the bad sector to be readable, so the harddrive can write the contents of the bad sector to the reserve sector and then swap it and hide it from the operating system. But it cannot do this if it has been too badly damaged. In that case you need to write to that sector so the harddrive skips the 'reading' part and can write straight to a reserve sector and remap it immediately. Such sectors are called "pending bad sectors" and are the most dangerous since those are not hidden from the operating system and can cause problems in Windows and other operating systems.