I have a legal copy of Windows Vista Home Prem 64-bit OEM in German. I am thinking about upgrading to Windows 7. I would like this time to buy an english version (Last time, I got a german by mistake). In Amazon:

* Windows 7 Home Premium 64 bits [OEM version](http://www.amazon.de/Windows-Home-Premium-Bit-englisch/dp/B002NGJO4M/ref=sr_1_2?ie=UTF8&s=software&qid=1260355146&sr=8-2) is 91,95 €
* Windows 7 Home Premium 64 bits [Upgrade Package](http://www.amazon.de/Windows-Home-Premium-Upgrade-englisch/dp/B002DGS81C/ref=sr_1_1?ie=UTF8&s=software&qid=1260354765&sr=8-1) is 119.99 €

Is it possible to upgrade from a german copy of Vista to a English copy of Windows 7?

OEM stands for "original equipment manufacturer". I guess since Amazon sells these copies, it must be legal for me to buy them. Moreover, since an operating system updates for free, I assume I would end with the same OS. 

Is there any differences bettween buying the Upgrade Packgage or the OEM besides price?