Inode error woes

[Piltdownster]

Got a PC which is dual-booting with XP. After installation of Ubuntu
everything was fine. But after a few weeks errors appeared (duplicated
inodes) which were apparently corrected by running e2fsk - but then they
reappeared. So, thinking it was a HD problem I installed a 2nd drive,
allowing Ubuntu to use it all. All was well for a couple of days, but now I
am getting a similiar problem. The precise error on boot-up is:

EXT3-fs error (device hdb1): ext3_get_inode_loc: unable to read inode block
- inode=2256577, block=4521990

Any ideas?

Thanks.