Splitting A Row In A Table Into 2 Or More Rows?

I am working on a project that requires to calculate interest on the amount. There are 2 tables, 1 with Interest rate for a product for different and periods and another is product table with amounts in different period.

Table 1 (Rates table)

Product From To Rate
1111 1/1/2012 1/20/2012 .75
1111 1/20/2012 1/28/2012 .50
1111 1/28/2012 4/6/2012 .40

Table 2 (Product table)
Product From To Amount
1111 1/1/2012 1/17/2012 10000
1111 1/17/2012 1/24/2012 15000
1111 1/24/2012 2/25/2012 20000

What i need to do is to calculate interset based on the above 2 table and insert into another table (Interest). However, the problem is with identifying correct rates for the periods in Table 2.

Eg.

for period 1/1 to 1/17: applicable rate would be .75

for period 1/17 to 1/24: From 1/17 to 1/20 the rate would be .75 and from 1/20 to 1/24 it would be .50

this is what i want to achieve, basically to split the period between 1/17 to 1/24 into 2 so that appropriate rate can be applied.