Сделать ключевой селектор, который превращает версию в число:
string[] versions = {
"7.5.0.17 Date: 05_03_10",
"7.5.0.18 Date: 05_03_10",
"7.5.0.19 Date: 05_04_10",
"7.5.0.2 Date: 02_19_10",
"7.5.0.20 Date: 05_06_10",
"7.5.0.3 Date: 02_26_10",
"7.5.0.4 Date: 03_02_10",
"7.5.0.5 Date: 03_08_10",
"7.5.0.6 Date: 03_12_10",
"7.5.0.7 Date: 03_19_10",
"7.5.0.8 Date: 03_25_10",
"7.5.0.9 Date: 03_26_10",
"7.5.1.0 Date: 05_06_10"
};
versions = versions.OrderBy(
s => s.Substring(0, s.IndexOf(' ')).Split('.')
.Aggregate(0, (n, v) => n * 100 + Int32.Parse(v))
).ToArray();
foreach (string s in versions) Console.WriteLine(s);
Выход:
7.5.0.2 Date: 02_19_10
7.5.0.3 Date: 02_26_10
7.5.0.4 Date: 03_02_10
7.5.0.5 Date: 03_08_10
7.5.0.6 Date: 03_12_10
7.5.0.7 Date: 03_19_10
7.5.0.8 Date: 03_25_10
7.5.0.9 Date: 03_26_10
7.5.0.17 Date: 05_03_10
7.5.0.18 Date: 05_03_10
7.5.0.19 Date: 05_04_10
7.5.0.20 Date: 05_06_10
7.5.1.0 Date: 05_06_10