Hi,
First is there anything that you need to do that cannot be done using Works?
If there is nothing that you need another "More Advanced" application to do then stick with what you know. I know a few people who have done this and are perfectly happy doing so.
At the moment I do not have access to an Office 2007 install but the space for OpenOffice 3.0 is 344 MB (361,484,288 bytes) Size on disk.
If all your colleagues are using office 2007 then there is something to be said for using the same, as this should totally eliminate any possible incompatibilities, however minor.
If however you just want to explore the possibilities of a more advanced system and as you have already tried Office 2007 I would suggest that you give Open office a go - The un-install options works
One other thing if you require experience with an office application for inclusion in a resume, then, at the moment, the M$ option would carry more weight.
This sort of choice is so subjective that the only person who can decide is the person concerned, the reason that one is preferred over another can be something as simple as the colour of a certain toolbar but that is still a valid reason.
Technically I believe that either application is capable of providing the tools to do the job.
Hope my ramblings help you make your choice