Indesign CS - Windows XP Professional - Athlon 2400 - 512M Ram

I have a simple 50 page manual (1 master page) broken up into 10 sections. I'm finding that if I add additional text or a graphic, the text/graphic layout on subsequent pages changes. How can I "anchor" the pictures at a precise point in the text and maintain layout of the text as it flows around the graphics?

The reason I ask is that the text and graphics are still being developed, and I want to maintain the layout of page 45, even if I add text or a picture on page 40 (same section).

The graphics are all approximately 3" x 4".

Thanks,
Al