OK I had this happen to me on my first house.
Went into contract to buy the house in 2009. Obviously I had the leverage here due to the market conditions. Basically freaked out because it was my house and I was 25 years old. I worked through it, did research, got estimates, worked with the seller and got a nice check at closing.
Basically in many cases a bowing foundation on a house is caused by poor drainage (as was the case here). So check that first of all. More often then not simply getting the water away from the house through gutters, drains, grading etc will prevent any future problems. Any interior work/bracing etc is for peace of mind and for resale.
About 4 years later I opted to sell the house as the market had gotten A LOT better and the show was on the other foot in terms of leverage. I had an offer quickly but it fell through I did disclose the foundation issue. Part was due to the basement foundation but the other was due to a MASSIVE mistake by the realtors agent. Basically the real estate agent put into the contract that the BUYER would pay her fee, and not the seller, so that was going to cost her the entire commission. Needless to say she killed the deal. Obviously an agent has a lot of sway over a single first time home buyer.
I got a second offer a week or so later, closed no problem.
In terms of selling I would disclose this early and often, that way there is no 11th hour freak outs by the buyer. YMMV.