Getting a curve to fit my points

[Bio-Hazard]

So, I have a table of data, and I'm trying to get a curve to fit the points.
I haven't tried excel yet, but I have tried these things:
1) Openoffice.org
2) Gnumeric
3) XMGrace

- Gnumeric was straight-forward, but lacked many abilities.
- Openoffice.org couldn't fit the curve well enough
- And XMGrace wouldn't consider the maximum Y-value as a graphing constraint.

So, I'm trying to figure out this:
How do I fit a decent curve to my graph while having the curve feature take consideration of the maximum and minimum y-values?

Take a look at this for more information:
http://www.oooforum.org/forum/viewtopic.phtml?t=88559

[CFDFEAGURU]

Are you trying to fit to linear or non-linear data? Also, dont assume a good fit simply by looking at the results. Always ask yourself, could there be a better fit than mine? Lastly, are you familiar with the Chi Squared method?

Thanks
Matt