The best i can say here is that i share your concerns.
First of all, you are correct that whatever brand of PC you order you will get pre-installed software. Also in the case of Acer this will be true. It is your choice however to decide if removing this unwanted software is faster and more easy then a complete re-install. My first guess would be removing the software, but thats my personal opinion of course.
Second: are you sure you will get an (oem) installation kit with win 7? I'm afraid Acer will give you certain driver cd's and additional software, and the pre-loaded win OS will be on a (hidden) partition.
Third i think it will not be possible to use a different win7 os version CD with an OEM installation key. I'm not sure about...