Seems like a good deal:
Samsung SpinPoint T HD501LJ 500GB SATA-II 16MB Cache - OEM £61.99 (£72.84)
Western Digital Raptor 74GB WD740ADFD 10,000RPM SATA 16MB Cache - OEM £86.99 (£102.21) Times two £173.98 (£204.42)
I'd be uneasy about screwing a friend over like that though. he should know that he could sell them second hand and perhaps get 2 500 GiB drives with the proceeds. If he accepts this and wants to go through with it anyway, go for it.