I want to start working with linux, and I know I should work in that regularly to improve myself.
I work with sql server, office, c# at the company. can I install and do my tasks in linux (i.e. red hat)?
You have three options:
3) Dual Boot
For C# development on Linux, Mono Project is the way to go. You can develop in MonoDevelop IDE and connect to SQL Server hosted in a virtual machine using SQL Client (for more info see: Mono/ADO.NET, Mono/ODBC, Mono/Database Access)
Also if you want to have the latest version of Mono and tools I recommend using openSUSE because thats the first place where you'll find the latest updates, Mono being a project backed by Novell which is the company that also sponsors openSUSE distribution.
EDIT: (Completing the Office part of the question)
// Office suites //
1) IBM Lotus Symphony -> http://symphony.lotus.com/software/lotus/symphony/home.nsf/home
2) Oracle OpenOffice -> http://www.oracle.com/us/products/applications/open-office/index.html
3) OpenOffice.org -> http://www.openoffice.org/
4) GNOME Office -> http://live.gnome.org/GnomeOffice
5) Go-oo.org -> http://go-oo.org/
6) SoftMaker Office -> http://www.softmaker.com/english/ofl_en.htm
7) KOffice -> http://www.koffice.org/
// Online Office suites //
0) Microsoft Office Online -> http://www.officelive.com/en-us/
1) Google Apps -> http://docs.google.com/
2) Zoho -> http://www.zoho.com/
3) ThinkFree -> http://thinkfree.com
4) Live-Documents -> http://www.live-documents.com/
5) Ajax13 -> http://us.ajax13.com/en/
6) ContactOffice -> http://www.contactoffice.com/
7) FengOffice -> http://www.fengoffice.com/web/
8) Zimbra -> http://www.zimbra.com/
Sadly, SQL Server is a Microsoft product, and I don't think they are stupid enough to support a platform that competes with Windows (i.e their bread and butter). Things that use SQL Server are hardly configurable to use another database server, and I don't think you can change it in your company anyway.
The same thing goes for MS Office (if you meant it). There are alternatives for MS Office, the most notable being OpenOffice.org, but no there won't be MS Office on any Linux (unless you plan to run it on WINE, which is quite cumbersome to setup or maintain, and there is no guarantee that it will work).
C# is a longer story. Still it's meant to be used on Windows (ask Microsoft for more information), but there is Mono, the opensource implementation of the .NET framework. There have been debates whether a Linux user should use it. Technically I can see a major obstacle when everybody else uses Visual Studio on Windows and you try to make it work on Linux.
I hate to say this but frankly, I don't think you should try to use Linux at your workplace. If you want to learn Linux (which I encourage), install a user-friendly distribution (Ubuntu maybe?) on your personal computer is your best shot.
@phunehehe and @ddeimeke have given good answers already. But I disagree with the statements on MS Office, yes there are alternatives (and it appears Go OO was left off), and wine, but I never see anyone mention Crossover Office. Crossover is a fork of wine that's commercially backed. If you really want to run Microsoft Office for professional use I'd try that. This may also allow you to use windows tools for SQL Server.
MS SQL Server is a windows application, which is designed to run on windows. Linux is not Windows. It is possible that there are some tricks to get it up and running on Linux, but I would not recommend it.
Mono is a C# and .Net development environment for Linux.