A test program, perfect in Earlier Version, but not 9. The problem is, how to do it with Mathematica 10 or 9?
Needs["PlotLegends"]
g1 = Plot[Sin[x], {x, 0, 2 Pi}];
legend = Join[{Graphics[{Thick, Blue, Dashed,
Line[{{0, 2}, {15, 2}}]}], #1} & @@@ {{Style[
"\[CapitalOmega]=15", FontSize -> 11,
FontFamily -> "Times New Roman"]}}, {Graphics[{Thick, Red,
Dotted, Line[{{0, 2}, {15, 2}}]}], #1} & @@@ {{Style[
"\[CapitalOmega]=20", FontSize -> 11,
FontFamily -> "Times New Roman"]}}, {Graphics[{Thick, Black,
DotDashed, Line[{{0, 2}, {6, 2}}]}], #1} & @@@ {{Style[
"\[CapitalOmega]=30", FontSize -> 11,
FontFamily -> "Times New Roman"]}}, {Graphics[{Thick, Black,
Dashed, Line[{{0, 2}, {6, 2}}]}], #1} & @@@ {{Style[
"\[CapitalOmega]=40", FontSize -> 11,
FontFamily -> "Times New Roman"]}}];
ShowLegend[
Show[g1], {legend, LegendPosition -> {0.5
, 0.25},
LegendSize -> {0.5
, 0.4`}, LegendShadow -> None,
LegendBorder -> None}]