There are several issues with your code.
Reference: PIC18F2455/2550/4455/4550 Datasheet, Section: 12.3 Timer1 Oscillator, Page: 133
12.3 Timer1 Oscillator
An on-chip crystal oscillator circuit is incorporated
between pins T1OSI (input) and T1OSO (amplifier
output). It is enabled by setting the Timer1 Oscillator
Enable bit, T1OSCEN (T1CON<3>). The oscillator is a
low-power circuit rated for 32 kHz crystals. It will
continue to run during all power-managed modes. The
circuit for a typical LP oscillator is shown in Figure 12-3.
Table 12-1 shows the capacitor selection for the Timer1
oscillator.
The user must provide a software time delay to ensure
proper start-up of the Timer1 oscillator.
Therefore configure Timer1, near the top of your program, before enabling any Timer1 interrupts. In other words, move the statement:
near the top of the code listing, followed by a sufficient delay to allow the Timer1 Oscillator to begin operating.
Also you have failed to enable peripheral interrupts by setting the PEIE bit, INTCON<6>, along with the GIE bit, INTCON<7>.
Therefore the Timer1 interrupt will not be triggered and the Interrupt Service Routine (ISR) will never be called.
Keep in mind the selection of caps for the 32.768 kHz crystal are dependent largely on the crystal's specs and not on any recommendation, therefore refer to the crystal's datasheet for the proper capacitor selection.
There maybe other issues, however the aforementioned came to mind.
BigDog