My system

Dell Inspiron 531 Athlon Amd x2 5000+

4GB RAM

320 HDD

2x DVD RW

XFX8600GT XXX

Windows Vista Premium

Hi

I have already added to my computer. It came with 1 DVD drive, 2 GB RAM and onboard graphics

I added a 2nd DVD drive 2x 1 GB memory sticks and the XFX graphics card.

In addition a TV tuner USB stick is connected to one of the ports.

So far no complaints. The system runs steady.

I want to add another HDD now and it will be a 400 GB 7200 3.0gb/sec SATA with 16MB cache

My PSU is 300W and - yes, I know - Dell's PSUs are stronger than they look and my unit can support more than 300W.

But as far as I understand a harddrive can be a hefty drain on a PSU and insufficient power can overheat the drive or cause it to fail.

How can I estimate or - better - make sure that I have enough juice left to support a second HDD?

Thanks