Just speculation, but I wonder if he isn't more worried about his hard drive than his monitor.
Given what he said, can we assume both the PC and the speakers are on top of the desk?
I think alignment is more important than distance. For example, if it is 3" from the bottom corner of the speaker to the top corner of the PC case, you are probably OK. However, if the speaker bass driver magnet is 3" from the side of the PC and right near the hard drive, this could potentially be a problem ... potentially.
So, what it gets down to is ...as it often does... we don't have enough information.
My apologies for the lack of pertinent information (yes they are on a desk).
Currently I have Wharfedale 9.1.s that are shielded, they are 115cm apart and 90cm from the floor (the tweeters are approx head height), the right hand speaker sits on a corner cupboard with my PC case, It's a very large case (and high spec) Antec p180. The speaker is toed in and away from the case, I would estimate the speaker magnets are about 10 inches from where hard disks are situated and probably the same distance to memory and CPU.
I generally feel better, and your explanation does help, but it is still not crystal clear exactly what is where.
Is there any change of the photo of the computer and nearby speaker, or a simply sketch to give us a more visual representation?
To give you a general sense of how distance can make a difference, let me relate my situation. I have some larger 12" woofers with 32 ounce magnets. At my old house, they sat a little higher than they do now. This place them beside my TV (CRT), near the bottom right corner, and I did get screen aberrations cause by the effects of the magnets.
In my new house, the speaker was still next to the TV, just on a different stand that placed it a little lower. The straight line distance of about 10" to the magnet was about the same, but it was now down and to the right. In this case, no problem with magnetic interference. So, subtle changes in the location can make big differences in the result.
Also, keep in mind that your computer cabinet represents a shield, and the hard drive itself is further shielded pretty substantially. So, you have a degree of protection.
So, my point is, very fine and subtle details make a big difference, so a photo or sketch could tell us a lot.
Have you used the speakers yet, and what is your impression of them? Always valuable information.
I haven't bought them yet I might go for the Monitor Audio BX2's which are shielded (but I would prefer the Dali Lektors).
I don't have a digital camera and my mobile camera is kaput (a picture says a thousand words eh?).
The offending speaker would be 3 inches away from the side of the pc case at its rear and about 5 at its front. The motherboard and its attached bits is over on the opposite side from the side that is next to the speaker. The speaker is raised up 6 inches on a wooden box and its top is level with the top of the pc case.