Looking to upgrade from integrated graphics on Dell Dimension 570

I have a Dell Dimension 570 - full specs:

AMD Athlon II X2 240 (2.8GHz, 2MB)
4 GB DDR3 SDRAM 1066MHz (3 DIMMs)
1 GB ATI Radeon HD 4200 (512 MB dedicated, 512 MB shared)
320 GB SATA II Hard Drive (7200 RPM)
16X DVD +/- RW w/dbl layer write capability
Windows 7 Home Premium
17 Inch Acer LCD - 1152x864

According to this, the system has a 300W power supply. I'd like to upgrade to something like the ATI Radeon HD6450 as shown here.

I figure this will be a nice upgrade - gaining graphics processing power on top of freeing up 512MB of system memory.

My question is whether I have a PCI Express slot or not, which the Radeon HD6450 will require - and whether my 300W power supply will be able to support the video card.

I'm not looking to run Crysis or anything like that. I'm aiming for improved overall performance, and a better DVD-viewing experience.

The specs page on the Dimension 570 says it ships with a PCI Express slot but I don't know if that only applies to current makes of the system. I bought this over a year ago.

So, do I have a PCI Express slot and will my 300W power supply cut it? Running Windows 7 64-bit with a dual boot Ubuntu partition, if that matters.

Hello, i'm pretty sure your PC does have a PCI-EXPRESS slot because this is a newer line and basically everything made after 2007 has one. But the best way to be sure is to open up the case and look for yourself. A PCI-EXPRESS slot will have a slot like this

The bottom Black one is a PCI-Express slot. and that Notch :
_______________
[----|----------------]

the | will be closest to the back wall of your case.

Also if getting a big GPU like that I recommend Getting a 500-600Watt PSU to run safely.