I don't think the Xbox price in Comet is a Microsoft price cut but a response to the offer in Dixons at the same price, but only when you trade in an old console first. I quote the advert by Comet in the Daily Express today:
"At Comet we don't do sales, short-term discounts or trade ins - we just have low prices everyday."
Thus the price of the PS2 is unlikely to drop as well unless of course Dixons extend their trade-in offer to it as well as the Xbox.
I believe the trade in offer is still going in Dixons. Today I saw an advetisment in the Daily Express for PC World ( part of the Dixons Group ) for the same trade in. The Comet offer did not require a trade in, but I am not sure if it is still going or if it was ever on their web site. The best thing to do is phone or visit your local Comet branch.