1997 pontiac Sunfire will not shift into gear. I can shift it by hand with the lever on top of the transmission but it still will not move. Is there a vacum modulater on this model of car?

Busted shifter cable , not moving shift lever out on the transmission . Your best bet , take it to a mechanic .

Automatic Transmission Shift Lock Control Description and Operation
The automatic transmission shift lock control system is a safety device that prevents an inadvertent shift out of PARK when the engine is running. The driver must press the brake pedal before moving the shift lever out of the PARK position. The system consists of thew following components:
• The automatic transmission shift lock control solenoid
• The body control module (BCM)
• The powertrain control module (PCM)
With the ignition in the ON position, battery positive voltage is supplied to the automatic transmission shift lock control solenoid. The automatic transmission shift lock control solenoid receives a ground from the BCM. When the automatic transmission shift lock control solenoid is energized, the shift lever mechanically locked in the PARK position. When the driver presses the brake pedal the PCM sends a class 2 serial data message to the BCM. The BCM turns OFF the ground control circuit and this de-energizes the automatic transmission shift lock control solenoid. When the automatic transmission shift lock control solenoid is de-energized, the shift lever may be moved out of the PARK position. The BCM determines transaxle shift lever position through a class 2 serial data message from the PCM. The PCM receives inputs from the park/neutral position switch and determines shift lever position. When the BCM receives this information and determines that the shift lever is out of the PARK position, the automatic transmission shift lock control solenoid ground is opened.

Do you know what a DTC is ? Diagnostic trouble code !

DTC B2708
The body control module (BCM) controls the automatic transmission shift lock control solenoid. Positive voltage is supplied via the ignition 1 voltage circuit to the automatic transmission shift lock control solenoid. The BCM controls the ground circuit of the automatic transmission shift lock control solenoid . When the brake pedal is depressed, the BCM removes the ground allowing the solenoid to disengage. This action allows the vehicle to be shifted out of the PARK position.
Conditions for Running the DTC
DTC B2707

Your best bet mite be to have a qualified repair shop check it .

Check that as you move the shifter, that the shifting rods beneath are moving in tune with the shifter's position.
If not, then your mechanism is faulty.
It is almost certain that the issue lies with the external shifting mechanism.
The issue may be just beneath the shifter lever, within the rubber or leather bag shroud. You might have to pull out the centre console to have a closer inspection.

No vacuum modulator on this transmission. Even if it did, a bad vacuum modulator only works during the 1-2 shift. It would not affect ability to drive from 0-mph

Sounds like transmission is low on fluid and gears are banging together when they shift. Probably should check the level and add to fill and hope that no damage has been done. I hope that helps you figure out your problem.

Maybe the mounting bracket that holds the cable to the transmission is different?

check the fluid in the slave cyclinder if its low it can cause this

Usually I find one of three problems that cause a manual transmission to be stuck in a single gear. If the gear oil level is low then the shift forks and rails can get dry and bind enough that the rail sticks and won't move. The same low fluid problem can cause the sliding gear to become stuck hard enough on the splined shaft it slides on that it won't move or the shift interlock parts between the shift rails [which prevent two gears from being engaged at once] can break or bind which will also prevent the shift lever from moving. The shift lever and tower [the part the lever is fastened to on top of the transmission] may have to be removed to see if the problem can be fixed from the top or if the problem is internal and the transmission has to be taken apart and repaired. There are other problems that cans cause this such as bad internal bearings, broken or worn shift forks but they are fairly rare if the oil level is maintained and changed occasionally.

What you can try is to remove the shift cables from the transmission side. then move the shifter and see if everything is free if it's still sticks then the cables are going to be replaced. if everything is moving with the cable off. then you need to remove the shift tower on the tranny (where the shift cable is I belive it's 5 bolts) remove the tower and you will see the shift pin. Inside the tower there is a cotter pin that breaks and that will cause you to have one gear and unable to selected another gear. If you are not mech inclined I would no attemped the shift tower repaire, the cables do it will save you money. The shift tower has bushings that can fall into the tranny.

Check the fluid level on your clutch slave cylinder. Have someone depress the clutch while visually observing the movement of the levers under the hood. Could also be a bad throwout bearing.