looks pretty good for a first site!
don't like the double underline on hover - one would be nicer
don't underline your headings e.g. Step 1: Placing your order.
because it looks ike a link. you could use a bottom border all the width of the main column instead.
why is it in frames? is that to do with your hosting?? if not then take it out of frames!
your product pictures are really important but they are crap.
use a better camera, take pictures against a white wall and then cut them out in photoshop or other image editor something like this
(although there's a limit to what i can do with that image grabbed off your site
)
as already mentioned, your images are too big! and you could present them with something like this -
http://www.huddletogether.com/projects/lightbox2/
if you can get hold of some better images and want to hire me to present them for you, cutout, levels adjusted, placed against a background and incorporated in a slideshow i'll do it for a very reasonable fee
otherwise if you feel you can do it yourself - or learn - then please do as your product images sell your products, and at the moment they are the weak part of your site! you want potential customers to say - 'wow - that looks cool, i want one',
not 'huh that's looks a bit naff and you can see all the mains cable and stuff on their desk/wall.
also when you take the photos and you have a shot like modded pc 7 (the one with red neons through big window) then take it slightly from the front so you don't see the back panel with all the leads and bits trailing out
using Zyminc and got my domain name from 123-reg.co.uk. 
