need FSCK help!

[Claude Jones]

I'm getting the following in my system log:

Oct  2 12:43:53 tehogee smartd[2509]: Device: /dev/sda, 1 
Currently unreadable (pending) sectors 
Oct  2 12:43:53 tehogee smartd[2509]: Device: /dev/sda, 1 Offline 
uncorrectable sectors

many, many, of them
/dev/sda contains my /boot and / mounts
/home is mounted on a separate drive

How can /dev/sda be "Offline" since this is the machine I'm typing 
this message on??? 

Is FSCK the right tool for this? If so, I can't figure out how to 
run it on /dev/sda since, if I read correctly, the mount has to 
be unmounted - presumably, I need to do this from a rescue disk?

I've searched on this in the past, but was never able to find a 
good explanation of how it's donw. If someone can give me one, or 
point to a good document, I would be grateful
-- 
Claude Jones
Brunswick, MD, USA