I take it that you are using the stock sprint rom? If so it can be done but is harder to do as you have to remove or disable the htcguardian.exe and do some regedits. With a custom rom its as easy as hooking up your phone via the usb cable and selecting the phone as a modem and the stock ics will connect and share the internet over the usb cable. With using the MacBook Pro instead of windows you will need the proper drivers for mac for the generic RDNIS driver.
There is also an ics.exe over on xda its called ics .21 that will let you do it over bluetooth/Wifi, However if you are not charging the phone you will kill the battery pretty quick and the speed is limited to 300kb/s (as its a limit of the bluetooth protocol). Wifi part is simple b4 u launch the proggy just go into network connections and setup an ad-hoc network make any name you want for the ssid, turn on wifi launch the ics .21 exe from the phone select tnet**11 as the private interface and the cellular line as public save settings then click start ics. Connect to the ssid on your laptop that you made on your phone. Let it connect and you will be online.
To flash to a custom rom is easy. If you want the stock feel but a great sprint rom try the Silence/Mighty colaberation. It is lean and mean runs everything screaming fast. No bloatware. Has the ics hack built in.
http://forum.ppcgeeks.com/showthread.php?t=43266 <- how to flash
http://forum.ppcgeeks.com/showthread.php?t=43266 <- How to flash from sd card. Your best bet bc you won't need a windows based pc to unlock or flash the rom to the phone.
http://forum.xda-developers.com/showthread.php?t=377047 <- ICS Control .21 utility and instructions.