For the WRS qualifier, you will only need to submit a reply if requested by a GTP Race Admin via PM. Since times for the qualifier must be kept secret, your replay should never be posted, and should only be sent directly to a race admin after receiving a request.
For WRS events, replay requests are made in the results thread, and replays should be posted in the results thread for review by other racers.
Winzip is not required to compress or post a replay, but can be used.
This post, from the IFTC event, details how to copy a replay to your computer and compress it. However, instead of uploading the replay to the GTRP database, you'll add it to your thread reply, by clicking on the "attachments" button (the little paperclip icon) in the tools pane of the reply dialogue.