7 & 8 Dual boot

2.8 MHz G840 - 4 GB DDR3 - 500 GB SATA hdd 7 + 8 upgrade disk

Can I partition my hdd 100 GB, 100 GB, Balance

Install a copy of 7 on both 100 GB partitions with the same cd key

Then upgrade one of them to 8 ?

Or would that cause problems as far as activation ?