Hi Tony
Desktop and Media centre PCs are also mounted horizontal and also have restricted space, but work without problems, so providing you don’t use the really high power CPU, (Keep to 95w or below) cooling is no problem. (You will find if you use an auto variable fan, (Or if AMD activate cool & quiet) it very seldom runs at anywhere near full speed)

Remember Wersi have a similar construction since 2000 (Uprated in 2003 with the introduction of the P4) and apart from a faulty batch of MSI boards, there have been minimal problems with factory built units. (The P4 was probably the hottest running CPU ever made)
Hope this helps to put your mind at rest

Bill


[This message has been edited by abacus (edited 06-01-2010).]