RTD Sensor Datasheet Details
The resistance is 1000\$\Omega\$ at 0°C. The sensors follow the DIN IEC-751 (European) RTD curve with \$\alpha\$ = 0.385 so at 100°C the resistance is 1385\$\Omega\$. 

You can either look up the table from various sources*, use the Callendar VanDusen equation to calculate R(T), or use the polynomial as described in the ITS-90 temperature standard. 

*If the table is given for a Pt100 sensor, just multiply the numbers by 10 for Pt1000. 

All DIN type platinum RTD sensors should follow the exact same curve, within the specified tolerances- that's a huge advantage of such sensors- they are interchangeable between sensors and between manufacturers of such sensors.  

Edit: Here is the Callendar VandDusen equation implementation for a DIN RTD: 


  double cvd(double t, double R0)
    {
    double A = 3.908E-3;
    double B = -5.775E-7;
    double C = -4.183E-12;
    return R0 * (1 + A *t + B * pow(t,2) + (t - 100)* C* pow(t,3));
    }  


t is the temperature (Kelvin) 
R0 is the resistance at 0°C

That results in the following results from 0..100°C


  For T =  0.00    R = 1000.00
  For T = 10.00    R = 1039.02
  For T = 20.00    R = 1077.93
  For T = 30.00    R = 1116.73
  For T = 40.00    R = 1155.41
  For T = 50.00    R = 1193.98
  For T = 60.00    R = 1232.44
  For T = 70.00    R = 1270.77
  For T = 80.00    R = 1308.99
  For T = 90.00    R = 1347.07
  For T = 100.00   R = 1385.02  


By the way, 1mA is a relatively large current for a Pt1000 RTD. You should check that self heating is not an issue.