Illustrator will certainly do in a pinch, but upgrading your version of InDesign is certainly preferred. I would talk to the printer you're having make the brochures to see which option they would recommend, and if they can print the job from an Illustrator file. Otherwise, you can always export the Illustrator doc into a PDF.
Check with your printer! If you're comfortable with Illustrator, it's very convenient to use that, but it's really not very hard to apply your illustrator skillz to indesign. I usually just design my graphic elements in illustrator, save them as eps, bring it into InDesign and do the text layout, and just tweak things back and forth as needed.
Many people have been clamoring for Adobe to add multi-page functionality to Illustrator, and, they finally did, they just put it in InDesign instead. haha
good luck
michael