I need a new AGP graphics card

I am one those people who still has an AGP based system. It uses a socket 478 motherboard equiped with a 3.2Ghz Pentium 4 CPU and has Hyperthreading enabled. Right now it does everything I need of it, and its pretty quick too. It runs Windows XP Home 32-bit SP3 and has 1792MB of DDR RAM installed. That odd number is made of up of the two original 512MB cards plus a 256MB card and another 512MB card both stolen out of my even older computer. I use 784MB of it as an NTFS ramdisk for the Windows pagefile, which is probably the reason for it being so quick. It may not sound like a lot, but I've never seen it use more than 70% of the pagefile, and the total RAM usage has never exceeded 85%.

I want to upgrade the graphics card though, as currently it is an old Sapphire Radeon 9600. The GPU runs with a core speed of 324Mhz and a memory speed of 189Mhz. It plays what I need it to play but not at the details I would like or as smoothly as I would like. The new graphcis card I am considering has a clock speed of 750Mhz and a memory speed of 1746Mhz. It also has 1GB of memory rather than the 256MB my current card has.

I was quite suprised when I found out that some companies are still making AGP cards using a modern GPU. I expect this already old computer (its been stood unsed for most of its life) to last me several years and it is stupidly quick compared to my older Celeron based machine. The CPU usage rarely hits 100% and usually only does so when starting up or when updating antivirus software and playing a game at the same time. Even then though, the slowdown is barely noticable. Heat buildup is not a problem as I've recently installed two 80mm case fans which has made a huge difference. The HDD sits at 34-38C while the CPU at idle sits at 26C and will peak at 42-48C when under load for lengthy periods.

This is the card I am looking at:

http://www.ebuyer.com/product/169945

My concerns though:

1. The PSU is only 300W, and although it is stable with the system as it is, Im not sure if it would cope with a new, higher power 70W graphics card. Also, I believe it has no PCI-E power connectors which I think the card will need. However, it does have two 4-pin molex cables spare and I know 4-pin molex to PCI-E adapters are available. Would I be better off replacing the no-name 300W PSU with say, an Antec EarthWatts 380W? I've never built a PC before and I've never messed around with PSU's either so I don't know how big of a job it is to replace it. Saying that, the PC was designed to be a multimedia PC that could be expanded.

2. Would my CPU be the bottleneck with this card installed? Its not worth spending £87 upgrading to this graphics card (£120 if I need a new PSU too) if my CPU will limit performance. Im not planning on playing games as demanding as Crysis but if a game comes out that I really want it would be nice to have a machine that can play it.

I supose the best way to test the power out is just to buy the card and try it. But then if I do need a new PSU I'll have to pay shipping on the PSU, which I won't if I buy both the card and PSU together (free shipping comes with the card, even bought on its own).