Yeah, I know about the trail you pick up over the tracks, but I just stick to Green Bay Road- it's a lot easier, plus I can stop at this Baskin Robbins shop if I'm feeling like I'd like a cone....

It's just past Glencoe, I think.
The trail that runs through Skokie lagoons (with the Skokie Sculpture Park, right?) doesn't ride alongside I-94. It's a bit farther east and runs alongside McCormick Road. You can backtrack from Foster Ave and catch the start of that trail there to Devon, then hop west on Devon to Caldwell and catch the Botanic Gardens trail at Caldwell and Devon, then ride the full 20 mile trail to Lake Cook Rd and Green Bay Rd. I guess you could also take the trail that runs along the lagoons to Golf Rd too, but then you'd be heading more eastwards, which would take you farther away from the Botanic Garden trail, and the hike from Golf Rd and McCormick Rd to Golf Road where the Botanic Garden would be a pain to hike over from.
I pretty much wing it- I don't know which trail or route I'm going to take until I get going and decide how I'd like to plan my pit stops. If I need lots of pit stops, I'm going the Botanic Garden route, and if I don't need as many pit stops, I'll take the McCormick Rd/Green Bay Rd/Sheridan Rd alternative and do the street thing.
Send me a pm sometime if you ever want to hook up for a ride...
Koffee