I think that the placement of RAM has been covered many times in numerous threads. Please do a search in the future.
From a search on the forums using the keywords "mac pro ram", on page 3, i found 2 helpful threads
https://forums.macrumors.com/threads/310864/
https://forums.macrumors.com/threads/303228/
and from the second thread, a very helpful diagram
http://homepage.mac.com/tribe3/.Pictures/MemConfig.jpg
I apologize if i have offended you but there have been many threads about the installation of 4 similar sized sticks of ram + 2x512mb sticks of ram which, even though may not be specific to your case of 4x1gb sticks of ram, can still be used as a guideline. Again, i apologize. And it's you're, not your.
For the record, I'm not offended. I don't get personally offended by text on a screen.
For the record, I'm not offended. I don't get personally offended by text on a screen.
For the record, I'm not offended. I don't get personally offended by text on a screen.