instead of select all just select what you need. If you have a monsterous usertable like vbulletin or other software does it is unneeded load to query the entire thing. Store that request data as either an array with two fields or two separate variables. No hard coding these values because you what it to be dynamic.

Code: Csharp
string uName = Request.Form['username'];

string passWrd = Request.Form['password'];
Code: SQL
SELECT usrname, password FROM login WHERE usrname = uName  AND password = passWrd;

or with an array.

Code: Csharp
string[] userCreds = { Request.Form['username'], Request.Form['password'] };

/* alternate way to do it
string[] userCreds = new string[2];

userCreds[0] = Request.Form['username'];
userCreds[1] = Request.Form['password'];
*/
Code: SQL
SELECT usrname, password FROM login WHERE usrname = userCreds[0]  AND password = userCreds[1];

Be sure to make a reference to System.Web and use it or else Request will not work.