Thought I would pass this tip along. I recently setup my parents computer with Open Office (WinXP too). My parents needed basic Office functionality, I was impressed with the Open Office suite. My Dad uses the envelopes feature the most. They had a HP 940 printer, which would handle printing envelopes. I was getting inconsistant results when getting it to work with one printer configuration.
What I wanted to pass along for others looking at Open Office, I created a ‘default printer’ option with regular settings. I created an additional printer setup to support Envelopes, which was pointing at the same printer. So inside Open Office, when I wanted to print envelopes, I chose the ‘envelope printer’. This worked liked a charm. I got the idea from a post here
Hope this helps.