A few questions

[Ondes 0]

When I started my city, my residential was across the river from my commercial. As I grew, I added residential nearby, although I probably should have done that originaly. Anyway, I have low customers on all my 3 types of commercial areas. I do have a mass transit subway system running through, but it doesn't help. There is also low commercial developpment, even with low taxes. Any ideas?

Related, some industrial is slow devlopping. I'd also like to attract more HT. 

And with cargo rail, where does the rail itself connect to the station? Same with the passenger station. I'm just not sure lol, played SimCity for awhile but just recently got back with SC4.

[Spinmaster 75]

Commercial: anything more than a taco stand or a Bob's Grease Pit requires education, particularly the pretty commercial offices. Aside from a few low-density neighborhood blocks, don't zone a lot of commercial until the demand is critical.

High Tech: requires education, and lots of it. If they're desperate enough, they will begrudgingly build in existing industrial zones, even with high pollution. But to get a lot of it ... best to separate it from the other industrial types by literally using taxes to keep HT out of one city, and ID & M out of another. You still needs lots of high education though (I think a college at-minimum is necessary) to get a lot of HT.

Rails: if you mean the in-game stations, the rails don't "connect" to the stations at all. Just run the rail alongside (i.e. "touching") the station on any side EXCEPT the side where the road must go.

For custom stations.. some are the same. If it has a track running through the station, connect your rails to it (drag the rails THROUGH it actually). If not, then run the rail next to the station, just as with the in-game stations. (Note: for the ones with tracks running through them, check the read-me carefully ... some are configured to ONLY allow passenger or freight trains through, not both - be sure to spur around it, or make the station itself a spur, if you're using the same route for both freight and passenger trains).