How do I select a TABLE row?

Use following command:

Set cell[Table Name, 0,row_number] "X"

Table name is displayed in the GuiXT screen elements view
0 is used for column as that is the only column that is selectable
row_number can be indexed i.e. you can use a variable for row number. Rows and columns are indexed from 0

Set cell[Table,0,1] "X"

Set V[idx] "1"
Set Cell[Table,0,&[idx]] "X" //This will set row number 1