wifi tethering is named as internet sharing in WP7 and yes focus has internet sharing facility but its blocked by default due to AT&T carrier, so you have two options:
1. custom rom: will take some time but custom roms come with a lot of features which will make it open like android instead of wp7/ios restrictions like bluetooth file transfer, file manager, directly installing ahem apps from phone browser etc etc..
[In short: install custom rom]
2. Windowbreak/jailbreak/rooting: you can go to
WindowBreak by WindowsPhoneHacker on your focus and it will automatically jailbreak your phone, then you can install/sideload apps from pc, the wp7 apps are in .xap format, install this xap
[XAP] Internet Sharing + Interop Unlock all-in-one for Samsung Phones - xda-developers and you will get internet sharing, apart from this you can install many other useful homebrew apps like wp7 root tools, marketplace config, bluetooth file transfer etc etc.
[In short: jailbreak your phone and sideload an app]