All you can get in the UK is the first season.
Vol. 1-4 each have 3 episodes on them
The final 4 volumes were released as 2 disc sets (Vol 5/6 and 7/
each containing 7 episodes.
The sales were flagging (not surprising really at £15 for 3 episodes which was the original release price) so they did the double volumes to just finish the season then they stopped releasing them.
HMV seem to have them in the sale at the moment (1-4 at £5 each and the double sets at £10) because of the movie.
There are no plans for the rest of the series in the UK that I'm aware of (maybe Fast Forward in the future as there's meant to be a push on that with all the new toys and a return to regular TV later this year but I wouldn't bet on it).
Atm the best way to get Seasons 2-4 is the US DVDs and Lost Season from Australia (though you would have to obtain the season 4 finale through other means).
My girlfriend got a great Multi Region DVD player off Amazon UK for £17 and that plays them all fine, so maybe look into that and you won't have to worry about the screen size of your PC.
If you have patience they are starting to do Season sets (well 1/2 season sets) in the US with Season 1 Vol. 1 and Season 1 Vol. 2 (all of Season 1 over 4 discs) coming in May and September this year. If you haven't got any of the DVDs and have patience I'd say that's the way to go and I'd recommend hidefdvd.com to get them from as the prices are cheap, the postage is reasonably priced and fast (and as a bonus the 1/2 season sets are cheaper enough that they would slip under the VAT radar). They have Season 1 Vol. 1 up for pre-order now (on page 5 when you search for ninja turtles).
The same site also has good prices on the individual DVDs (just be careful how many you order at once if you want to avoid VAT, over £18 gets charaged VAT so balance out the lesser postage from a bulk buy and how much VAT would be to work out the best option) though some are currently out of stock. They also have all the old series DVDs as well.
Hope that helps.