I know this is an old post, but as time moves on it will probably become more relevant. I just upgraded by Linkstation HS-DH500GL to a 2Tb hard drive. I used the Western Digital Caviar Green (Model WD20EARS) - it's quieter and uses less power!
This was the process:
1) Download "Hirens Boot CD"
2) As this is a ZIPped file you need to extract the .ISO file (in XP/Vista/Windows 7 just double click the downloaded zip)
3) Burn this to a CD - (if you are not sure how, download CDBurnerXP)
4) Once you have these files, remove the hard drive from the Linkstation. There are two screws on the bottom, and one at the back to remove the cover. Then there are 5 screws to remove the caddy from the rest of the system (two on the side, two on the top, and one through the fan.) Then remove the old drive from the caddy (6 screws - four on the bottom and two on the side).
5) You now have your old drive, and the new 2Tb. So connect these to SATA cables on your PC. If in any doubt disconnect other drives, but leave a CD or DVD drive connected, so you can boot from it.
6) Insert the Hirens Boot CD you created earlier and boot onto it.
7) From the initial menu choose Mini Linux
8) From the Applications Menu, Choose Partitioning Tools, and select G4L (Ghost 4 Linux)
9) Select RAW mode, select source drive (obviously the smallest), select the target (obviously the largest), the click clone - now wait (about 2 hours).
10) Reboot the PC when finished, and boot back onto the Hirens Boot CD, and Mini Linux.
11) Now choose gParted from the same menu.
12) Resize the Extended Partition, then resize the XFS partition in there. Apply and wait (about 10 minutes).
13) Put the new disk back in the caddy. Screw it all back together, and enjoy the 1.5Tb of extra space! :smileyvery-happy: