Leigh,
1) Make a copy of the auction list on your PC called something like "Vic_Auction_YYYY-MM-DD.xls" where YYYY-MM-DD is the date. (Today would be 2003-05-28. You don't have to format the dates in this - technically called "ISO" format - but they always sort correctly in a folder listing, whereas putting them in English format "d/m/yy" never does. It also means you have a backup if you accidentally bugger up the original file.)
2) Reply to the original thread including this file as an attachment.
3) When the thread is refreshed with the new post on the bottom, delete the older post that had the list attached (which will also delete the attachment that went with it).
The trick here is to avoid putting any important text on the post that has the attachment, since it will be deleted. If you have general info about the auction, post it in a separate reply to any that have the auction list attached.
Hope that's clear as mud
RET