Federal Estate and Gift Tax Regulations are found at 26 C.F.R. Chapter 1, Subchpater B (Parts 20 - 27).
The first number of a tax regulation indicates what kind of tax the regulation deals with. The number 1 at the beginning of a regulation identifies an income tax regulation (e.g., 1.2-1, Tax in case of joint return of husband and wife or the return of a surviving spouse); 20 an estate tax regulation (e.g. 20.2011-1, Credit for State Death Taxes); 25 a gift tax regulation (e.g., 25.2503-3 - Future interests in property).
The Code of Federal Regulations can be found on Lexis, Westlaw, and Bloomberg Law (law students and faculty have individual passwords for each of these subscription databases). Hein Online, which also contains the Code of Federal Regulations, is available on campus via IP address and off-campus via the OSCAR record. RIA Checkpoint requires individual registration for off-campus use, but is available via IP address on campus. CCH IntelliConnect is currently available for on-campus use only, with individual registration required.
The Mabie Law Library has print versions of the official version of the Code of Federal Regulations (which is updated annually). Estate and gift tax regulations are also found in CCH Federal Estate and Gift Taxes, Code and Regulations (updated to 2010 only), Law Stacks, KF 6571 A29 F4.
Free versions of U.S. federal regulations, including Estate and Gift Tax regulations, are available on FDSys.gov and via irs.gov. Although these are both government websites, the regulations found there may not be currently updated.