I invested with a group in a company about ten years ago. I bought 100 shares at $1,250 per share. Since than the company has lost value due to foreign competition. The shares are now worth $1.00 each. How can I deduct these taxes off my incime tax. Or can I use these loses against my 401k when someday I retire?
Tom::

At this point these are "paper losses," so there is nothing to deduct. However, if you sold the shares to someone at $1 each, you would then have a realized loss, and you would report the sale on schedule D as a long-term loss. You can use up to $3K per year in losses to offset income in calculating your taxes. If your total losses in a year are more than $3K, you carry forward the unused portion to offset gains in future years.

I don't understand your question about your 401(k) - were these shares that were purchased as part of your 401(k)? If not, then one has nothing to do with the other, except to the extent that realized capital losses can be used to help offset income, including income from your 401(k).