Printing: Better to print at low PPI or interpolate?

That's the question for the day. . .Had my D70 a couple of weeks now and there's a photo I'd like to print for my wife for mother's day. Since a D70s NEF size is equivalent to pretty much an 8x10 at 300ppi, if I want to print it 11x17 or 13x20 would I be better off printing at a low ppi (I think it would work out to around 200 for an 11x17) or upsampling the image to that size, at 300ppi, using Phoshop's "Bicubic smoother" option (that is the one that's best for enlargements, right?)? Anyone with suggestions will be appreciated. Oh- I've heard people say that the subject matters, so fyi it is a portrait of my daughter, and it will be printed at a lab on a lightjet. . .
Thanks,
Chip

My and my friend both do this (I have a Canon 300d, he has a Nikon d100)

Get your image from the RAW at 300dpi, thats 8x10 like you said.

Do whatever effects you want.

Upsize it by 110%... should go about 6 times til it's at 13x19.

Then, we sharpen, and print. I print exclusively from my Rebel at 13x19 at 300dpi and it is always awesome. Using an Epson 2200.