How high can I upgrade?

I have gotten hold of an older computer, and have decided that I would take it home and use it for a media center PC rather than sell it.
It is one of the older Compaq Evo's... black with the lower face panel silver... has a Pentium 4 1.7GHz CPU, 400FSB, has 512MB PC133 SDRAM, and 120GB ATA133 and 200GB ATA133 IDE HDD's.
The socket on the mobo seems to be a normal socket 478, but it doesnt have the black square heatsink retainer most S478 boards have. Instead, it has a round heatsink, that attacted directly to the socket, sort of like the old socket A and socket 370 boards did...
What this means is that I don't have any bigger, better HSF's to go on it, and I do have a faster CPU I want to put into it, but dont know if this HSF can cool it, I want to install a P4 2.6 400FSB Northwood into it... I am assuming it will work, as the board doesnt appear to have any jumpers, it "should" automatically take any 400FSB P4 I put in there, right?
Anyone have any experience with these old systems and know what that HSF can handle??
Thanx for the help!
-D

I would personally just keep it as it is the spec is fine for a media centre atm but you will obviously need an agp video card of some description a radeon 9550 for £20 would do. Alternitively you could sell the mobo and processor on ebay and buy a new 478 mobo 512mb ddr ram and a heatsink so you can fit your own northwood in and oc it to around 3ghz which is more than enough imo. Hope this helps.

The 1.7 gig Willamettes came in 2 flavors, socket 423 and socket 478. If it is socket 478, the chipset might or might not support the newer Northwood processors. Does the motherboard have a model number printed on it anywhere? Maybe use CPU-Z to see what chipset it has, like 845 or something similar.

Will try and find out chipset tonight. I had a Radeon 9800XT AGP card that I had put back in the case that I would need it... and when I got this PC set up a few days ago, popped my XT in there, and now whenever you start any kind of 3D app, like a game, the objects have "spikes" protruding off of them... sort of like peices of broken glass... so I am assuming my card got bent or something, and broke some pixel pipelines or something... so now I have a puny little GF2 MX200 32MB in the just to be able to use the thing, am in the process of trying to trade someone out of a 9800 Pro ATM.
Thanx for all the help so far guys! I know the P4 1.7 is probably fast enough, I just hate knowing that I have faster CPU's lying around that could be in there

You could always water cool it.