Probably the most correct PSU calculator you can use for MSI K8N Nvidia Neo's

Question

Syar & Shanks PSUCalc
Given the issues we see in the forum from lack of understanding of power supply requirements
& the variation in users experiences, Syar had the original idea to setup a PSU Calculator & invited me to get involved.
The result is an Excel Spreadsheet
For Pre Office 2003 
Download Link - PSUCalc - PSUCalcv1.82.xls
For Office 2003
Download Link - PSUCalc - PSUCalc2003.v2
Features:-
1) Select CPU
2) Select Gfx Card Press SLI button if applicable.
3) Allows for Overclocking impact By:-
Selecting CPU Voltage, Lower CPU Multiplier, Select Htt/FSB speed.
4) User Selectable Power supply Load target. For PSU to run efficiently, Quietly & cooler
It can't run @100%, generally accepted load Target is 80% of Maximum.
5) Enter PSU Specs by rail. The spreadsheet will then indicate wether the PSU is acceptable.
6) Variable Load calculations - Enable impact of idle & different % component activity to be seen. Graphics has (L)oad (3d) & (I)dle (2d) settings - All others on % load.
7) Enter Inputs in Colour Coded Cells.
The Spreadsheet uses US/UK Formating & so does not conform to European conention eg 1.56 US/UK to 1,56 Europe. To get round this European users should:-
Point to programs - Microsoft Office - Office Tools - Languages
Then set office language as us-English or uk-english as default .
Inside excel select tools - options - international-tab
Remove the tick on "use system separators" and enter . as the separator in the "desimal separator" box .
As somebody said Quote
Uk and US is as far  as i know the only countrys in the world using . as desimal seperator .
For anyone interested comments are around that show the basis of key calculations. CPU values have been derived from.
1) AMD Athlon™ 64 Processor Power and Thermal Data Sheet
2) Thermal and Electrical Specification of 8th generation AMD Processors
Thanks goes to Carlsberg without it this project might have been a lot harder  

Answer 1

PSUCalcv1.8
This is an update of the pre 2003 version.
THe major change is the addition of a Component Detail section below the Main screen similar to that found in the 2003
version.
Without VBA the lists used in the 2003 version using Data verificartion cannot be dynamically updated. So the Component Detail section in this version allows the user to enter data for specific components themselves.
This means that you have thae ability of getting a fairly accurate estimate of power usage using the default power settings, which will be adequate for troubleshooting PSU Issues or helping to choose a new supply.  By entering custom data a very accurate model can be created.
The accuracy basically revolves around how average is an an average(ok whats the SD for statisticians) This is best shown with an example. This is the List in the 2003 version all of which can be specifcally selected. in this version only a single value can be selected :-
Hard Drives           3.3v   5v   12v
all WD Caviar Sata   0.00   4.00   5.40
Generic PATA           0.00   8.00   17.00
Generic SATA           0.00   4.00   8.00
Maxtor DM10            0.00   4.29   7.95** Used as Default
Maxtor DM9/DM10 sata   0.00   4.29   7.95
None                   0.00   0.00   0.00
Seagate sata 120gb   0.00   4.50   8.00
WD raptor           0.00   3.50   4.20
So to take an extreme example if using 2 Generic Pata drives the default will understate consumption etc.,
To set up Cusytom user data:-
1) Enter Description
2) Select component Category using the row list selector & choosing:-
GFX   Graphics Card
CPUF   CPU Fan
FAN   Fans
CD   Dvd/CD
HD   Hard Drives
PCI   PCI/PCI-E
This ensures that the component is added to the relevent category in the summary sheet.
2) Enter the Watts used for the component (Normal running/Load) 3.3v,5v,12v.
3) Enter Number of the component used.
4) Optional Select Variable load %
As in the previous version you can use the default values However the entry point has now moved from the main form to the summary section of the component detail section. Just enter the number of items against each category.
CPU Fan
Fans
Dvd/CD
Hard Drives
PCI/PCI-E
The Variable load % for default components are in the orange user cells in Column L of the summary sheet as b4.
Summary :-
If you haven't got office 2003 or don't like to many lists & buttons This is the version 4 you.
2003 has more inbuilt component choices & data lists can be easily added.
The Same Set up steps need to be taken
1) Non US/UK - regional windows settings other than us/uk
2) Excel Addins