Clueless about spd's

I've always ridden with toe clips, but my knees are acting up, and I need to get some spd type shoes, to straighten out my weird riding habits.
I've been given some crank brothers smarty eggbeater stylee pedals and all I need are the shoes now. Preferably mountain bike ones as I am lead to believe they are easier to walk in when not clipped in.
I know nothing of these things, and I am very very poor, so £60 absolute max. Any recommendations? Bad experiences? things to look out for? Previous threads I haven't found yet? And what is 'float' and why is it so good?

Shimano M076

hope your a size 10
http://cgi.ebay.co.uk/Sidi-cycle-shoes-size-10-shimano-pd-m515-clip-pedals_W0QQitemZ250417457336QQcmdZViewItemQQptZUK_Sporting_Goods_Athletic_Shoes_ET?hash=item250417457336&_trksid=p3286.c0.m14&_trkparms=72%3A1688|66%3A2|65%3A12|39%3A1|240%3A1318|301%3A0|293%3A1|294%3A50

don't get multi release cleats if you buy shimano.

true dat

http://www.sbrsports.com/1011/892-211374 They look fly too!

Really?...

This is the Forum Help and Testing Area, why is this thread here?

Is this a new place to ask biking questions, and move away from How The Forum Runs Technically questions?

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£46.99 from wiggle.

Come up pretty snug, though so might be best to upsize.