Jason Cawley
Wolfram Science Group
Phoenix, AZ USA
Registered: Aug 2003
Posts: 712 
First, this forum is meant for New Kind of Science discussions. General Mathematica questions are better directed to Mathgroup, which you can find from here 
http://forums.wolfram.com/mathgroup/
Second, I'm not sure what you are trying to do, but an example might be all you need. If so, here is one 
mysolution = NDSolve[{x'[t] == y[t]  x[t]^2, y'[t] == 2 x[t]  y[t], x[0] == y[0] == 1}, {x, y}, {t, 0, 10}]
That returns an interpolating function object, stored in the variable name "mysolution". ParametricPlot needs to be called in a form that gives it an {x,y} value for each value of its parameter variable, which you can get from e.g. 
ParametricPlot[{x[t], y[t]} /. mysolution, {t, 0, 10}, PlotRange > All]
Note the construction /.mysolution . Interpolating function objects are effectively rules to replace their LHS variable names with tables of data. "/." means "ReplaceAll", meaning apply the following rules wherever their LHS's occur in the expression preceding.
Occasionally it may help to wrap the function Evaluate around the first argument in that call to ParametricPlot  from {x[t] to the end of mysolution in the line above, inside the brackets of the Evaluate  but it is not necessary in simple cases.
I hope this helps.
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