If you need to download the Windows XP service packs (SP1, SP2, SP3) now that the XP support date has ended, you can still download them from Microsoft. Links to each are on this page:
http://windows.microsoft.com/en-us/windows/service-packs-download#sptabs=xp

XP SP1:
http://www.microsoft.com/en-us/download/details.aspx?id=19751

XP SP2:
http://www.microsoft.com/en-us/download/details.aspx?id=28

XP SP3:
http://www.microsoft.com/en-us/download/details.aspx?id=24

If you can not use the EA Download Manager or are unable (or unwilling) to install the incremental updates manually, there are “super” patches available officially from EA which will update you to the newest version from any version of the game.

These patches are listed on the Sims3 online forum, located here:

http://forum.thesims3.com/jforum/posts/list/175477.page

The “super” patches are about 400MB.

The manual incremental patches are available here:

http://forum.thesims3.com/jforum/posts/list/188505.page

For the purpose of archiving, at the date of December 19th, 2010 the following “super” patches were available at these links:

(region instructions further down)

Region 1
http://akamai.cdn.ea.com/eadownloads/u/f/sims/sims…s/TS3_1.18.9.009001_Update.exe
Region 2
http://akamai.cdn.ea.com/eadownloads/u/f/sims/sims…s/TS3_1.18.9.009002_Update.exe
Region 3
http://akamai.cdn.ea.com/eadownloads/u/f/sims/sims…s/TS3_1.18.9.009003_Update.exe
Region 5
http://akamai.cdn.ea.com/eadownloads/u/f/sims/sims…s/TS3_1.18.9.009005_Update.exe
Region 7
http://akamai.cdn.ea.com/eadownloads/u/f/sims/sims…s/TS3_1.18.9.009017_Update.exe

Find out your region by navigating to C:\Program Files\Electronic Arts\The Sims 3\Game\Bin and open “Skuversion.txt”
Do NOT change anything in this file. The last number in “Game Version” indicates your region. For example:
GameVersion = 1.12.70.006001
This game version would be region 1.