Lots of upgrades...not so much information...

Okay, i've had my Dell Dimension 4550 for a little over a month and a half now.  And it is coming to that time when i need to upgrade some of the less useful parts in my system.  However, it seems the tech support goons refuse to supply me with the information i need to do these upgrades.  I know all about how to do this stuff, I just need some information (i almost do this for a living).  Anyways, i'm going to throw in another hard drive and raid the 3 drives in the system, put in a Radeon 9800 Pro 256MB graphics card, and add in a few more small bits.  But, this poses a few problems, firstly, the dell power supply (which is weak to say the very least) wont support this kind of extra load.  I added 2 40mm fans to my pc (on top of the current gfx card, and the NorthBridge which was quite toasty to say the least) and the psu is already putting out a considerable amount more heat.  So the obvious solution is to upgrade to a better powersupply.  I was thinking of somthing in the 400-550watt range.  But, due to dell being a company that thrives on being very proprietary, the connector on the dell mobo is not standard.  The goons at tech support also tell me that my motherboard "will not support a bigger power supply" when i know this is total bull.  Is there some sort of Dell -> ATX Standard adaptor out there i can get?  But, Adding in the powersupply and extra drives ect also poses another problem...The dell case is WAY too small to support all of this stuff, so, the solution to this is that i must buy a bigger case.  This shouldnt be a problem, however i'm not sure if the dell mobo will fit in a standard atx case, As i need the extra bays and hard drive space for the new components.

Any information reguarding these issues would be appreciated, along with perhaps any good 400-550watt powersupplys that are engineered for quiet use, that i may be able to use.

So, here's a quick recap of what i need to know:

1.) Dell Powersupply ----> Upgrade version? Dell to ATX standard adaptor available?

2.) Dell Mobo -----> Will it fit correctly into an ATX standard sized case?

3.) I know i diddnt mention this, but is my dell motherboard's AGP port capable of handleing a radeon 9800 pro? or is this also underpowered like so many other dell products are?

-Any information would be greatly appreciated.

---Thanks in advance,

------Pig