i'm a mac/wintel/linux/novell user... wintel/linux/novell at work wintel/mac at home...
imho... transferring files between the two systems is so easy. Adobe files are compatible on both systems. I work in a company that has a lot of graphic designers, they all use Macs. The managers and other departments are on PC's. When they have to view Photoshop/Illustrator files from the designers, they just e-mail it or transfer it on the network and they're good to go. No hassle or anything. And as to the price / performance ratio (most especially in the graphic design), you can get a better deal on getting a mac than a pc.

the ibook is a lower end range for laptops on the mac. (i.e. max ram of 1.2 gb compared to the 2gb for the powerbook, slower speed, lower bus, lower vid card, etc.). for more info check out http://www.appleclub.com.hk/ go to the store section and you'll see all the specs.

for your needs though, an ibook with maxed out ram would probably suffice. and it's a lot cheaper to get it here in HK, no tax. unlike in manila there's VAT.