Aligning ragged text columns

Can anyone please suggest how I can print:

a <- matrix(c(
	"Heading 1",  "This is some info\nabout heading 1",
	"Heading 2",  "This is some info\nabout heading 2",
), byrow=T, nrow=2)

to look like:

Heading 1  This is some info
           about heading 1
Heading 2  This is some info
           about heading 2

(if you're not using a fixed width font, I want the text in the second
column to line up)

I've looked at encodeString and format, but neither seems to quite be
the right tool

Thanks!

Hadley