6600 GT and ACOF

I am going to buy this card but I have a couple of scenarios:
First My PC
Dimension 8200
P4@2GHZ 400FSB
768MB RDRAM@ 400MHZ
Geforce Ti4400
The mobo is AGP 4X
1) Can I buy a 6600GT AGP for this PC (the mobo is not 8x). Will reduce its speed to 4X?
2) Does my PC is prehistoric or it can handle another 1.5 year of games?
3) Did the 6600GT will make and incredible performance boost over the crappy 4400?
4) Will you spend 1100$ on a new PC or buy the card, sacrifice performance, but then buy a super faster PC 1.5 years later.
5) Does the 4X AGP will slow the card too much?
First My PC
Dimension 8200
P4@2GHZ 400FSB
768MB RDRAM@ 400MHZ
Geforce Ti4400
The mobo is AGP 4X
1) Can I buy a 6600GT AGP for this PC (the mobo is not 8x). Will reduce its speed to 4X?
2) Does my PC is prehistoric or it can handle another 1.5 year of games?
3) Did the 6600GT will make and incredible performance boost over the crappy 4400?
4) Will you spend 1100$ on a new PC or buy the card, sacrifice performance, but then buy a super faster PC 1.5 years later.
5) Does the 4X AGP will slow the card too much?