Can you post your fstab so we can give you real world examples?
A generic idea:
/dev/hda1 is Caviar A in Windows. In Linux, it set it up arbitrarily to /dev/hdb1 as Caviar A. You want /dev/hda1 as Caviar A and need to tell fstab so. Your current entry would look something like:
/dev/hdb1 "/mnt/Caviar A" vfat option1,option2,and,so,on 1 1
And you would modify it (not just the order):
/dev/hda1 "/mnt/caviar A" vfat option1,option2,and,so,on 1 1
Note the /dev difference.
As for what umask does:
One way to grant permissions on any given file or directory is to run the command chmod. Umask is the 'equivilent' (not really, but for simplicity we'll take that) of chmod, but using the opposite numbers. So, a chmod of 777 will grant the earth permission on that file, while a umask of 000 will do the same thing.
Not exactly a complete definition of umask, but a usable one
For more info you can always check out the docs on chmod and mount.