How is this working...?

Hello. I'm about to upgrade my computer, which I've scavenged parts for for a few years.. Originally the case I had came with a power supply. That burned out, so I had an old 350W Dell laying around from one of my parent's computers. I put that in.

However, I realized just yesterday, it's freaking 350W, and I've used this computer to do CAD with (Solidworks and AutoCAD, both newest versions), play Crysis, etc.

Hardware:

Mobo: Intel DG965WH (LGA 775 socket) Desktop board
CPU: Intel Core 2 Duo E6400, 2.13 GHz
Ram: Corsair (2gb) and Kingston (2gb) (kingston pieced in later)
GFX: PNY Verty 9600 GSO (has 6 pin supplemental connector)
HDD: WD Caviar Black 1TB and a 500Gb
DVD: (2) Liteon DVD Burner 24x- IDE connection at the time
OS: Windows 7, 64 bit
Creativ sound card add-on

Essentially, shouldn't this need at least 450 to run stable? (I'm just rounding in my head). Or is it just an intrinsically stable build that is not as fast as it could be, being short on power? Running at PSU Max capacity? I have no idea.

I have new hardware ordered (MSI Z77 Mpower, i7 3770K, and 8Gb Corsair Vengance), and I'm going to have to upgrade the PSU anyway because I need more SATA power ports. But for theory, I am very curious to know whether this build has more potential but lacks power, or just is a really low draw system.

I thought you usually get a blue screen with low power?