as a designer i would use Quark or Indesign as a layout programme. You can export print-ready pdfs along with bleed and crop marks that the printers need. There's a lot more to sending stuff to print that just having it 300dpi.
here's a link of the top ten things you'd need to check...
[broken link removed]
here's a link of the top ten things you'd need to check...
[broken link removed]