Produce the chart from the data from your first workshet. Go to your second
worksheet, select the relevant data, copy, go to your chart, edit/ paste
special, and accept the relevant option to add a new data series or add data
to an existing series.
Alternatively having produced your original chart, go to Source Data, and
either adding data to an existing series or adding a new series will allow
you to select the relevant data from whichever worksheet.
Note, however, that if you really have more data than will fit onto one
worksheet, it may not fit on one chart either. Looking at "limits" in help
for Exvcel 2003, here are some examples:
"Data series in one chart: 255"
"Data points in a data series for 2-D charts: 32,000"
As one worksheet in Excel 2003 can have 256 columns & 65536 rows, you may
struggle with your chart if your data goes beyond that.
Limits in Excel 2007 are greater, of course.