Dell Inspirion 660

Hi guys,

 I just purchased a dell 660 desktop (core i5-3330).  I understand the power supply is only 300w and the 660 inspirion chasis is a mini tower ? correct me if I am wrong.  

Any will most aftermarket power supply units fit inside of the 660 or will I be limited by the size of tower.

also the main reason to change the psu would be if I decide to get a better video card. (mid - high end video card)

this brings me to the next question about graphics.     (i've narrowed it down to either a radeon7850 + new psu or just a new 7750 - either case the prices of video cards should go down hopefully over time)

but i'd like to know the following: 

1. Does the dell 660 (core i5-3330) have intel hd graphics 4000 or 2500 as standard?

2. Is the dell inspirion 660 considered a mini tower? If so will it still accomodate a regular sized radeon 7750. I understand the 660s slimline is limited to a low profile card, however can the regular 660 chasis accomodate a normal sized radeon 7750.

3. There are a few 7750 cards with a passive heatsink instead of a fan on the gpu. (ex. sapphire Ultimate 7750). Does the addition of the heatsink will mean that the space of Two slots will be taken up. Can the 660 chasis still accomodate  this type of card.

4. If I open the desktop chasis to install a new 7750, will it void the warranty on my system?

thank you all for the information.