[Community] line_locate_point() in Python, and general confusion of a GIS newbie

[Michael Elsdörfer]

I'm pretty much a beginner when it comes to GIS, but I think I 
understand the basics - it doesn't seem to hard. But: All these acronyms 
and different libraries, GEOS, GDAL, PROJ, PCL, Shaply, OpenGEO, OGR, 
OGC, OWS and what not, each seemingly depending on any number of others, 
is slightly overwhelming me.

Here's what I would like to do: Given a number of points and a 
linestring, I want to determine the location on the line closest to a 
certain point. In other words, what PostGIS's line_locate_point() does:

http://postgis.refractions.net/documentation/manual-1.3/ch06.html#line_locate_point

Except I want do use plain Python. Which library or libraries should I 
have a look at generally for doing these kinds of spatial calculations 
in Python, and is there one that specifically supports a 
line_locate_point() equivalent?

Thanks for your time.

Michael