It's not free but you can add an MP3 convertor to Windows Media Player. In media player, go to the tools menu, select download and then plugins to be taken to the relevant site. Choose MP3 creation and voila!
The MP3 encoder is just under $10 (not sure how that converts into sterling but it's not that expensive). You can then set up media player to copy files automatically whenever a cd is inserted - it will even label them correctly using info from the internet - or just choose which ones you want manually.