XNA - continuous obstacles accross the screen

Hello,

Im in the process of making a frogger style game, xna is brand new to be, ive a basic map with a movable character, i guess the next stage is to have obstacles / cars continuously streaming across the screen. but ive no idea where to begin.

i know how to get a car across the screen once the game begins, but once it leaves the screen should i have it immediately return to the other side and loop, or have some sort of random number to wait and then repeat the process.

any advice / bits of code / or ideas of code i should explore are more than welcome. thank you.

Regards
Ryan

random is always fun to me :P

i did this once with birds in the background
i just picked which side it would come with a random 0 or 1 and a timer with a random interval and when the timer was greater then the random time would make the bird cross the screen. when it got past the other side just get another random 0 or 1 and another random interval and wait for that one to run out and so on

this was pretty simple and was just back of a background but wouldnt think it'd be hard to do with other things but i know nothing of xna

GameDev.net - all your game development needs is a good source for XNA related questions. This is a C++ Game programming forum and is not the best place to ask XNA questions.