Just use Genuine Fractals trial version, good up to 20 images (then it stops). For really big prints (and even upsizing to e.g. 400 dpi Noritsu prints at 30x40cm), it works better than just plain bicubic. Or at least use Lanczos interpolation (in freeware IrfanView), it's quite better than just bicubic as well.
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