ok work out how much money you think the business will make each year, then work out how much mone they are going to have to invest at the beginning to set the business up.  divide the money you think it will make by the money they need to invest.

Eg they will make $40K sales in the first year, there will be $35k expenses in the first year so te business will make $5K

to set up the busiiness they need to buy xyz so will put in $100K (this is called equity)

5/100 = 5% return on investment for the first year.

hope that helps

on god i'm a geek

Return on investment is the money you can expect back on capital used to start up teh business.  Normally most start up business do not expect to see a ROE in the first 3-5 years.  Basically if you have projected your income and expendture for the first 5 years in the business plan then uses this to calculate your anticipated profit, divide tis by the equity in the business and you get the return on investment, normally this would be referenced to money in bank return rates.