imac vs hp t3470

I'm currently updating my home computer system and am seeking some advice. I've been a pc user for many years (mainly adobe cs, premiere, microsoft office, messenger, itunes and firefox) and am not sure whether to invest in the hp t3470 for £735 (Intel® Pentium® D Processor 930 Dual core, 2 x 3 GHz, Level 2 cache 2 x 2 MB, 533 MHz. 360 GB 7200. Intel® 945P express chipset. 1GB RAM. 9in1 memory card reader. 256 MB video memory. 7 USB 2.0 ports (3 in front); 2 FireWire-IEEE-1394 ports (1 in front); 1 parallel port) or the 20" imac with educational discount.

Are these similar systems?

Is it time to swap to mac?

I'd appreciate any advice.