Use crystal or oscillator ?

Yes, you could for some devices like the MSP430F5438A.  Fnd "Crystal Oscillator, XT1, High-Frequency Mode"  In newer devices XT1 is reserved for low-frequency operation, and XT2 can be available for high-frequency operation.  Devices like the MSP430F5342 work like this.

I question the need for an external crystal that fast though.  For many applications the internal DCO is good enough for active mode operation.  One example where the application demands a high frequency crystal is if you want to make use of the USB on a device like the MSP430F5528 where you would need a crystal of at least 4 MHz.

Reference: USB Module > USB Operation

Sunglin Chen said:

Could I use an oscillator with higher frequency,

Most MSPs support a so-called bypass mode for the XT1/XT2 crystal inputs.
In bypass mode, you pass a TTL-level square-wave signal into the inut pin. The output pin is unused.
The G2xx series and some other MSPs (all those who do not support a high-frequency crystal) officially only support 50kHz as input signal. But experiments have revealed that higher frequencies are accepted fine even on those.

Sunglin Chen said:

What is the difference between the crystal and the oscillator?

A crystal is the frequency-controlling part of a crystal oscillator. (other oscillators use R/C or L/C combinations, current sources or whatever).
The remaining part of the oscillator is built into the MSP (a so-called Pierce Oscillator). It is basically an inverter with adjustable output current. If you attach a crystal, the whole thing oscillates. And teh mechanical dimensions of the crystal's Quartz core control the frequency (like the length does for a clock pendulum).

An external oscillator includes all this: inverter, crystal, locad capacitances etc. It requires a supply voltate and emits a square wave signal of a fixed frequency (well, there are adjustable types too, which are way more complex internally)