Audio question - mic-in/line-in

[Michael Murphy <murphymichael@netscape.net>]

I'm shopping for a new laptop.  My current toshiba laptop's sound card
(ymf754) lacks a line-in jack which results in badly overdriven audio
at even the lowest mixer setting when doing such things as
transferring lp's to cd's.  

There seem to be very few notebooks which have a line-in jack, but
more which list a combination mic-in/line-in.  For instance, the acer
aspire 1520 and the asus Z9000 both seem to sport this feature.  Do
these ports automatically detect the line level and self adjust?  Is
it purely a hardware feature or is special support in linux required?  

I'm clearly no audio engineer and would appreciate the guidance of
others.  
-- 
Michael