The Taxpayer Relief Act of 1997 includes new estimated tax provisions that may let you hang on to more of your money during 1998:

Safe Harbor Modified for High-Income Individuals. Prior to 1998, the required annual estimated tax payment (to avoid an underpayment penalty) for high-income individuals was 90 percent of the current year’s tax liability or 110 percent of the preceding year’s tax liability, whichever was less. The definition of a high income individual for this rule was and remains as follows: an individual with adjusted gross income (AGI) of more than $150,000 (or $75,000 if married filing separately) for the preceding tax year.
Individuals above the threshold who expected a raise often took the simple approach and calculated their payments based on 110 percent of the prior years’ tax. However, for 1998, estimated tax payments can be based on 100 percent of 1998 tax liability. Don’t get too used to the break, though. It pops up to 105 percent for 1999 through 2000, 112 percent for 2001 and 110 percent for 2002. For individuals with AGI below $150,000 (or $75,000 if married filing separately), the required annual payment remains as it was under prior law: 90 percent of the current year’s tax liability or 100 percent of the preceding year’s tax liability, whichever is less.

De Minimis Threshold Increased. Prior to 1998, individuals did not incur a penalty for underpayment of estimated taxes if their total tax liability for the year, less withholding and estimated tax payments for that year, was less that $500 (or if the estimated satisfied the IRS’s safe harbors). For tax years beginning after December 31,1997, this threshold is $1,000.