adobe photoshop - Large Format Photograph Printing

I've got a client who wants me to create a large format banner to go hang at the rear of his property. The bulk of this banner is a photograph of his shop, with some text at the top.

For the photograph element, I'm finding that the images he supplied are looking hideously pixelated and noisy when viewed at 100% in photoshop. So I'm thinking I will need to get some more photographs taken.But, I only have a 6mp camera at present, and am not sure if this will be enough.

The photograph will be printed to a size of approximately 189cm(high) * 254cm(wide), and the overall image sent to the printers will be at 150dpi.

This leaves me with two questions:

1) Is there a way to get better results with photos in this scenario than simply 'Place Embedded' and the stretch to size?

2) If I need to take new photos, will a 6MP image be sufficient? If not, what sort of MegaPixels will I need?

I realise this is a bit of newb question, so please let me know if the question can be improved, and what info is needed, etc.

Thanks in advance!