Did you try adding the -c
parameter?
Excerpt from wget manual:
-c
--continue
Beginning with Wget 1.7, if you use -c
on a non-empty file, and it turns out
that the server does not support
continued downloading, Wget will
refuse to start the download from
scratch, which would effectively ruin
existing contents. If you really want
the download to start from scratch,
remove the file.
Also beginning with Wget 1.7, if you
use -c on a file which is of equal
size as the one on the server, Wget
will refuse to download the file and
print an explanatory message. The same
happens when the file is smaller on
the server than locally (presumably
because it was changed on the server
since your last download
attempt)---because ''continuing'' is
not meaningful, no download occurs.
On the other side of the coin, while
using -c, any file that's bigger on
the server than locally will be
considered an incomplete download and
only "(length(remote) -
length(local))" bytes will be
downloaded and tacked onto the end of
the local file. This behavior can be
desirable in certain cases---for
instance, you can use wget -c to
download just the new portion that's
been appended to a data collection or
log file.
To my knowledge it should skip files that are already downloaded and of the same size.