Dell 1905FP problem resolved
Update: the problem I was having with bleached-out highlights and minty pale greys on my Dell 1905FP was solved by switching from my MSI mobo's onboard S3 Unichrome VGA to an nvidia FX5200 on DVI. The FX5200 on analogue input shows the problem a bit, but not as badly as the Unichrome. The FX5200 on DVI gets rid of the problem completely. The DVI image is perhaps a tiny bit clearer, but the main difference is in tonal range on highlights and neutrality of pale greys.
I'm guessing that my Dell's analogue input is a rogue sample, difficult to drive or plain faulty. I haven't seen other reports of the minty pale grey problem with the 1905FP but there's been the odd report of washed-out colours, so anyone experiencing this with the analogue input might want to try DVI. Hope this helps someone and thanks to everyone who contributed to this thread. I think we're all happy punters now!
Dave