Help w/ updating Graphics/changing power supply.

I need to get a mid to high range graphics card into this Dell Inspiron; here's what I'm working with:

Pentium Dual Core CPU E6700 @3.2 GHz
PCI-E Gen.2 G43T-DM1 V:A00 mobo
4 GB DDR3 RAM
1 TB (2 x 500GB)
Windows 7
Integrated Graphics (for the moment)

AND, a big hiccup in this process, a HIPRO 160W PSU. SO, obviously, that will need replacing.

My question is, without changing anything other than the Power Supply, am I limited to what Graphics Card I can put into this system based on the other components? The mobo? Everything is housed in one of those Fat, squatty, Dell Inspiron towers.

I need something at least around Radeon HD 7770+ or GeForce equivalent.

Also, do the listed components restrict me to a particular max watt power source?