no usb network during install and corrupt packages

[Paul S]

I have an older laptop that I am trying to install xubuntu on a 4 GB usb 
pendrive.

The network fails because the installer does not recognize and setup 
eth1 by the usb cdc_ether driver.  This driver works fine on another 
laptop.  So, I have to proceed without network.

Next problem is that during base system installation, I get an error 
message "warning: 
file:///cdrom/pool/main/i/iputils-ping_20071127-1_i386.deb was corrupt" 
and it tries to fetch a good package, but fails with the message 
"Warning: Couldn't download package iputils-ping".  This is repeated for 
many packages and I have to abort the installation.  I have repeated 
this process 3 times with the same results .. everything works ok until 
I am installing the packages.  I also tried this with kubuntu and get 
the same complaints of corrupt packages.

Now the funny business:

1. a "media check" shows the disk is good ("The CD-ROM integrity test 
was successful.  The CD-ROM is valid.").  This was run on the same 
laptop and cd player.

on a different laptop and cd player where I have linux already installed:

2. mounting the cdrom and running "md5sum -c md5sum.txt" reveals no errors.

3. I install from the same cd media onto the same pendrive and get no 
errors saying defective packages exist.

Anyone know how to get the usb ethernet driver working with the 
installer or how to overcome the corrupt packages messages?