apt-get update error

[Tez]

Hi,
This isn't a huge problem but it gets annoying.
When I do a "sudo apt-get update" everything goes fine except when it
gets to
http://archive.ubuntu.com dapper/main Packages
It says:
gzip: stdin: not in gzip format
Errhttp://archive.ubuntu.com dapper/main Packages
  Sub-process gzip returned an error code (1)

And at the end it says:
Failed to fetch
http://archive.ubuntu.com/ubuntu/dists/dapper/main/binary-i386/Packages.gz 
Sub-process gzip returned an error code (1)
Reading package lists... Done
E: Some index files failed to download, they have been ignored, or old
ones used instead.

This has been going on for a while now, but the odd thing is if I do:
"wget
http://archive.ubuntu.com/ubuntu/dists/dapper/main/binary-i386/Packages.gz
-O -|gzip -dc > filename"
it works fine, no errors.
What command dose apt-get use to decompress the Packages.gz file that's
not working?

Anyway It's more of a curiosity since updates are in the dapper-updates
repository which works fine, it's just confusing to me.

Tez