Well..... That is MUCH harder then I think you might think... If you think it is ONE code thing, like dbMakeobjectSolid, your wrong...
I might not be the best person at explaining this, but I try it-
First, you have to download sparky's collision, it is really easy to use, and is really helpful. (If you need help placing the .lib file and the .h file- tell me.)
You can't really make an object a solid, you have to make a code that says, when this object collides with the wall, go back to the spot it was before it hit the wall.
Try doing this by your self, it is always better to get it working by yourself. The information I gave you I think will help.
If you are really stumped, check out jason's oop library, it is really good and helpful. http://code.google.com/p/darkgdkoop/downloads/list
At the bottom, there is a folder that is Sparky Config how to... Open that and debug that. Then, study the code.
p.s.- the sparky's thing was made when I asked this quesion, multiple times...
those links are--
http://forum.thegamecreators.com/?m=forum_view&t=128321&b=22
http://forum.thegamecreators.com/?m=forum_view&t=128400&b=22
http://forum.thegamecreators.com/?m=forum_view&t=128414&b=22
http://forum.thegamecreators.com/?m=forum_view&t=128461&b=22
http://forum.thegamecreators.com/?m=forum_view&t=128480&b=22
http://forum.thegamecreators.com/?m=forum_view&t=128872&b=22
I asked so many questions on doing this! I would say, if what I said doesn't help- these will, because they taught me....
~~Its not about what you know, its about how you figure it out.~~