Dell Windows Vista OEM to Windows 7 Upgrade

I recently bought a DELL STUDIO 1555 on June 12.
Since Free windows upgrade is for the systems purchased after June 26 i am not getting a upgrade.

I am from INDIA. I contacted Dell Customer Service here. They said i cannot purchase it from them also. Actually they had very less information about Windows 7. All they just said is that since my system is bought before June 26 i am not eligible. They had no further information about it.

I have Two Questions
Q1. Why Can't i purchase OEM version of windows 7 from DELL?

Q2.Since my laptop is shipped with OEM version of WINDOWS VISTA HOME PREMIUM 32 BIT SP1, if i purchase a WINDOWS 7 HOME PREMIUM UPGRADE PACK from Microsoft / Amazon etc,.
Can i install it on my machine ??

Can i install WINDOWS 7 by formatting C Drive or should it be installed over Vista ??

A1. Because OEM versions are only to be sold with a new machine.

A2. Yes, of course you can use the upgrade on Vista OEM.

A3. That's unknown at this point.

Actually I think Dell, HP, etc use Volume licensing. You can buy OEM but it is supposed to be sold with a computer part, a jumper wire is frequently thrown to meet the technicality. OEM is tied to one PC and there is no support from MS like with the full Retail version.
Joe