See red above for response.OEM:
1. Microsoft owns your copy of Windows not you. You purchased the copy as a "manufacturer"
2. Tech support. No tech support because you're a "manufacturer" and will provide own support.
3. Can only be installed 1x. Cannot be installed on a latter date on a different computer. Kind of... in most cases yes, but people have stated that this rule is pretty liberal at times.
Retail:
1. You are considered the builder of the computer and own the copy of Windows not Microsoft. No. You bought it as a customer of Microsoft and follows all retail purchase laws in your country.
2. No tech support. Yes tech support. Also normally costs more than OEM due to this nature.
3. Can be installed on a diffferent computer if needed in the future. Yes that is correct.