Based on the assumption you are working with Ubuntu
In most cases native open source alternatives are available and can be installed using the Ubuntu Software Center
Installing Software in Ubuntu
http://www.psychocats.net/ubuntu/installingsoftware
If you want to run a specific Windows app. then WINE which is a Windows Compatability Layer is a possibility however this method should not be relied upon
Using Wine on Ubuntu
http://www.psychocats.net/ubuntu/wine
Here is a list of Windows apps. which will run on WINE
http://www.psychocats.net/ubuntu/installingsoftware
Wine Application Database (AppDB)
http://appdb.winehq.org/
A better solution would be to grab a copy of XP and install it on a virtual machine. I thoroughly recommend VirtualBox which is easy to use and incredibly versatile
VirtualBox is available in the Ubuntu Software Center as outlined earlier in my answer
Installing Windows XP as a virtual machine on VirtualBox
http://www.ghacks.net/2009/06/15/installing-a-windows-xp-as-a-virtual-machine-on-virtualbox/
XP performance on a virtual machine is quite acceptable based on allocating 1gb RAM and 128mb Graphics
Install VirtualBox Guest Additions as well which wll give you additional features
Install Guest Additions for a better VirtualBox experience
http://www.ghacks.net/2009/06/17/install-guest-additions-for-a-better-virtualbox-experience/
Ubuntu 10.04 (Lucid Lynx) User Guide
http://ubuntuguide.org/wiki/Ubuntu:Lucid
Ubuntu 9.10 (Karmic Koala) User Guide
http://ubuntuguide.org/wiki/Ubuntu:Karmic
LUg.