st: linear spline and interaction

["stata_user stata_user" <stata_dofile@hotmail.co.uk>]

Hi,
I have used the follwoing code to test the associaton between z and y

mkspline z1  a  z2 = z,marginal
reg   y  z1 z2

predict p
label variable p  "L_Spline_a"

The first line creates a linear spline at the value 'a' of the variable z 
and then I use the result in the regression ( line 2)

My question , how I can include an interaction term with a dummy variable  
d?  the code

xi: reg y  i.d*z1   i.d*z2

does not give me the expected result

Thanks a lot for any comments

Sami

_________________________________________________________________
Windows Live� Messenger has arrived. Click here to download it for free! 
http://imagine-msn.com/messenger/launch80/?locale=en-gb

*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/