string ss = "0000001.003";
  float s = Convert.ToSingle(ss);

------解决方案--------------------
int a = Convert.ToInt32("00001");

------解决方案--------------------
int a = Convert.ToInt32("00001");  


或者 replace

------解决方案--------------------
string ss = "0000001.003";
string result = Regexp.Match(ss, @"(?<=0*)\d\.{0,1}\d+$").Value;

------解决方案--------------------
楼上正则帝

------解决方案--------------------
修改下：

(?<=0*)([123456789]+\.{0,1}|0.)\d+$