Using the Year() function will always get the current system Year.

You can join both pieces together using String Concatenation.

="ECO" & Year(Date()) & "-" & Nz(DMax("[ECO Number]","ECO Table"))+1

Now it doesn't do 001, it will just do 1, 2, 3...
Is that required?

You can use the Format function to get 0s. Will it only ever go to 999?
  Format(FIELD, "000")
You may need to wrap it in a CStr to convert it to a String.
  CStr(Format(FIELD, "000"))

So this may work, it's not been tested.

="ECO" & Year(Date()) & "-" & CStr(Format(Nz(DMax("[ECO Number]","ECO Table"))+1, "000"))

Alex