In regards to your questions about cutting straight, it is most likely an issue with the tension of the pinch rollers not being adjusted correctly. Try tightening these. In addition, make sure that the rollers are near the edges of the material you are trying to cut (and not in the breaks between the rollers).
With Flexi, you shouldn't need any Windows drivers, you should select "Roland PNC 1000" as the cutter model and then select the appropriate port. We have responded to your support emails asking for your phone number so that we could help you resolve any issues immediately. I think if we can talk on the phone, we can get you up and running in no time.
- Marcus