I am unable to figure out what your problem is and I think it is because of the description. I am supposing the stalling and the transmission and clutch behaviour are not related, but can't tell yet.
Can you drive this car at all? Does the transmission shift gears when you move the lever and it just feels wierd? Or are you unable to get the car into gear at all? And, forgive me if this is obvious, but when you step on the clutch and push it to the floor, did you say the car stalls? Is the transmission in neutral when this happens? I guess so, or you would be moving when the clutch pedal was pressed to the floor. Is this the case (that you are moving and then step on the clutch and the car dies)?
If the car dies when running as you step on the clutch, you may need an idle adjustment to raise the idle slightly so it does not stall.
IF the transmission shifts, but feels like it is not connected to anything, there are some bushings and parts that contribute to the precision feel of the shift lever's motion that may be gone or too worn to help, as M.B. Doc noted. Sometimes the little levers (more like reach rods that go from the gear selector area to the transmission, which is well forward of the shift lever) fall off when the connections are shot, and then you typically cannot move the shift knob at all as the mechanism gets jammed when the first lever drops on the others. The quick temporary fix is to find the loose lever(s) and connect them again, knowing they will fall off again, shortly. The real fix is to replace the missing or worn parts. If only one lever is off the problem is much easier to do without getting all the way under the car. If you manage to get more than one off, it takes a little longer to figure out what is what.
Hope this helps, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)