In this time of job changing and downsizing, you will probably need to know what to do with your company sponsored retirement plan at least once before your retirement. Once you leave a job for whatever reason, you need to make a decision as to what to do with your retirement plan. You can either choose to rollover the plan into an IRA or take the lump sum and pay the tax and penalties. Some companies also allow you to leave the retirement plan intact until you reach retirement age. This article discusses the choice of a rollover into a traditional IRA.
If you create a separate IRA for your rollover, you can easily move these funds to another employer sponsored plan in the future if the company allows this. It's a good idea to keep your rollover IRA separate from any other IRA's you might have because once you make contributions to a rollover that are not from a company sponsored plan, you lose the right to move this rollover to a company sponsored plan.
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I suggest you consult an investment manager who can assist you to identify your risk profile. (how much risk you are willing to take with investments), your overall financial situation, Personal tax implications etc.