To be perfectly honest, many of the tips I could offer here have already been posted on The Sims 2 official website. To save space, you can read them here.
At this point, I can offer some additional pointers.
When they say to confine your buildable area to the middle half of the map, they are not kidding. One of the first maps we created involved a wide river running through the middle and placing the town roads on one of the river banks near one of the sides. After importing the terrain into TS2, we could effectively only build on one or two streets, leaving the rest as empty avenues, because the game would not let us reach those other streets without using the free cam. You cannot place lots while in free cam mode.
A lot of the neighborhood terrains we have seen on other sites are built with roads going all over the map. They may look nice, but your maps will not allow that many lots to be placed on them.
Your best bet is to design your terrain along the edges extending inward only about a quarter of the way across and leave the middle flat and level (or slightly hilly, if you prefer) to build your town. This way, you can maximize your lot placement area and still have a decent looking neighborhood.
Regarding the custom neighborhood picture for your terrain, the best place to take the picture is within The Sims 2, not SimCity 4. Import your finished terrain into TS2, create a new neighborhood and enter it. Before you place any lots, use the free cam to position yourself where you have the view you want and take the shot. Once you do, exit the game, find the pic and open it in your photo editing software.
(If you don’t have any photo editors, we suggest Adobe Photoshop or Jasc Paint Shop Pro for high-quality editing. Most, if not all, scanners for sale today come with some sort of photo editing software package. However, some free programs exist on the internet, such as GIMP for Windows. About.com lists what they consider the seven best free photo editing programs. Check them out.)
Once you have the pic loaded, make sure the image size is 300 x 225 pixels, which is the size for the neighborhood pics used by the Maxis neighborhoods. Save it in PNG format named the exact same way as your terrain (Example: the picture for Pleasantville.sc4 should be Pleasantville.png) and put it in the same folder as your .sc4 terrain file, C:\Documents and Settings\[User]\My Documents\EA Games\The Sims 2\SC4Terrains. Why do this? The picture you created will come up every time you select the terrain when creating a new neighborhood instead of getting that green grid pic. If you wish to keep the neighborhood you created to make the pic, then copy the pic to where Maxis suggests.
If you want to include a bridge in your terrain, only certain types will carry over. The only one that has worked for me thus far is the level road. The tips from EA say that others will work, but I have had no luck with any others. If you want to avoid any frustration, just go with the one that works and use the level road bridge.
Do you have any additional suggestions, send us an e-mail! We’d love to hear what you have to offer.